WIP kind of
{ There's most likely a lot of BS, math people pls send me corrections, thank u. ~drummyfish }
Numbers (from Latin numerus coming from a Greek word meaning "to distribute") are one of the most elementary mathematical objects, building stones serving most often as quantitative values (that is: telling count, size, length, order etc.), in higher math also used in much more abstract ways which have only distant relationship to traditional counting. Examples of numbers are minus one half, zero, pi or i. Numbers constitute the basis and core of mathematics and as such they sit almost at the lowest level of it, i.e. most other things such as algebra, functions and equations are built on top of numbers or require numbers to even be examined. In modern mathematics numbers themselves aren't on the absolute bottom of the foundations though, they are themselves built on top of sets, as set theory is most commonly used as a basis of whole mathematics, however for many purposes this is just a formalism that's of practical interest only to some mathematicians  on the other hand numbers just cannot be avoided anywhere, by a mathematician or just a common folk. The word number may be the first that comes to our mind when we say mathematics. The area of number theory is particularly focused on examining numbers (though it's examining almost exclusively integer numbers because these seem to have the deepest pattern related e.g. to divisibility).
Let's not confuse numbers with digits or figures (numerals)  a number is a purely abstract entity while digits serve as symbols for numbers so that we can write them down. One number may be written in many ways, using one of many numeral systems (Roman numerals, tally marks, Arabic numerals of different bases etc.), for example 4 stands for a number than can also be written as IV, four, 8/2, 16:4, 2^2, 4.00 or 0b100. There are also numbers which cannot exactly be captured within our traditional numeral systems, for some of them we have special symbols  most famous example is of course pi whose digits we cannot ever completely write down  and there are even numbers for which we have no symbols at all, ones that are yet not well researched and are only described by equations to which they are the solution. Sure enough, a number by itself isn't too interesting and probably doesn't even make sense, it's only in context, when it's placed in relationship with other numbers (by ordering them, defining operations and properties based on those operations) that patterns and useful attributes emerge.
Humans first started to use positive natural numbers (it seems as early as 30000 BC), i.e. 1, 2, 3 ..., so as to be able to trade, count enemies, days and so on  since then they kept expanding the concept of a number with more abstraction as they encountered more complex problems. First extension was to fractions, initially reciprocals of integers (like one half, one third, ...) and then general ones. Around 6th century BC Pythagoras showed that there even exist numbers that cannot be expressed as fractions (irrational numbers, which in the beginning was a controversial discovery), expanding the set of known numbers further. A bit later (around 100 BC) negative numbers started to be used. Adoption of the number zero also took some time (1st use of true zero seem to be in 4th century BC), with it first just having a limited use as a mere placeholder digit. Since 16th century a highly abstract concept of complex numbers started to appear, which was later (19th century) expanded further to quaternions. With more advancement in mathematics  e.g. with the development of set theory  more and more concepts of new kinds of numbers appeared and still appear to this day. Nowadays we have greatly abstract numbers, ones existing in many dimensions, capable of counting and measuring infinitely large and infinitely small entities, and it seems we still haven't nearly discovered everything there is to know about numbers.
Basically anything can be encoded as a number which makes numbers a universal abstract "medium"  we can exploit this in both mathematics and programming (which are actually the same thing). Ways of encoding information in numbers may vary, for a mathematician it is natural to see any number as a multiset of its prime factors (e.g. 12 = 2 * 2 * 3, the three numbers are inherently embedded within number 12) that may carry a message, a programmer will probably rather encode the message in binary and then interpret the 1s and 0s as a number in direct representation, i.e. he will embed the information in the digits. You can probably come up with many more ways.
Order is an important concept related to numbers, we usually want to be able to compare numbers so apart from other operations such as addition and multiplication we also define the comparison operation. However note that not every order is total, i.e. some numbers may be incomparable (consider e.g. complex numbers).
Here are some fun facts about numbers:
quaternions . imaginary line
projected : (imaginary numbers)
projected j line 2i ~+~ ~ ~ ~ ~+ 1 + 2i
k line : : ,
... :_ : , complex numbers
\___ \_ j : ,
\___ +_ i ~+~ ~ ~ ~ ~+ 1 + i
+___ \_ : ,
k \___\_ : ,
\_\_: 1 2 3 4
  ~~~~~~~~~~~+~~~~~~~~~~~~~~~~~~~  
2 1 0: 1/2 , phi e pi real line
= i^2 : = 0.5 , ~= ~= ~= 3.14... (real numbers)
: , 1.61... 2.71...
i ~+~ ~ ~ ~ ~+
: 1  i
.
Number lines and some notable numbers  the horizontal line is real line, the vertical is imaginary line that adds another dimension and reveals complex numbers. Further on we can see quaternion lines projected, hinting on the existence of yet higher dimensional numbers (which however cannot properly be displayed using mere two dimensions here).
The following is a table demonstrating just one way of how you can play around with numbers  of course, we have generated it with a program, so we also practice programming a bit ;) Here we just examine whole positive numbers (like number theorists would) up to 50 and take a look at some of their attributes  we count each one's total number of divisors (excluding 1 and itself, 0 here means the number is prime except for 1, if the number is highest in the series so far the number is called "highly composite"), unique divisors (excluding itself), minimum divisor (excluding 1 except for 1), maximum divisor (excluding itself except for 1), sum of total and unique divisors (if the number equal sum of unique divisors, it is said to be a "perfect number"), average "dividing spread" (distance of each tested potential divisor's remainder after division from half of this tested potential divisor, kind of "amount of not dividing the number") in percents, maximum dividing spread and normalized range between smallest and biggest divisor expressed in percents (1 if there are none). You can make quite interesting graphs from similar data and discover cool and interesting patterns.
{ Be warned the following is just me making some quick unoriginal antiresearch, I may mess something up, it's just to show the process of playing around with numbers. ~drummyfish }
number  divisors  divisors uniq.  min. div.  max. div.  divisor sum  uniq. div. sum  avg. div. spread (%)  max div. spread (%)  div. range (%) 

1  0  1  1  1  0  1  0  0  1 
2  0  1  2  1  0  1  0  0  1 
3  0  1  3  1  0  1  0  0  1 
4  2  2  2  2  4  3  33  100  0 
5  0  1  5  1  0  1  16  50  1 
6  2  3  2  3  5  6  43  100  16 
7  0  1  7  1  0  1  24  66  1 
8  4  3  2  4  10  7  44  100  25 
9  2  2  3  3  6  4  36  100  0 
10  2  3  2  5  7  8  40  100  30 
11  0  1  11  1  0  1  34  80  1 
12  5  5  2  6  17  16  53  100  33 
13  0  1  13  1  0  1  35  83  1 
14  2  3  2  7  9  10  43  100  35 
15  2  3  3  5  8  9  44  100  13 
16  7  4  2  8  24  15  49  100  37 
17  0  1  17  1  0  1  38  87  1 
18  5  5  2  9  23  21  47  100  38 
19  0  1  19  1  0  1  42  88  1 
20  5  5  2  10  23  22  51  100  40 
21  2  3  3  7  10  11  45  100  19 
22  2  3  2  11  13  14  43  100  40 
23  0  1  23  1  0  1  42  90  1 
24  8  7  2  12  39  36  55  100  41 
25  2  2  5  5  10  6  45  100  0 
26  2  3  2  13  15  16  45  100  42 
27  4  3  3  9  18  13  44  100  22 
28  5  5  2  14  29  28  49  100  42 
29  0  1  29  1  0  1  45  92  1 
30  6  7  2  15  41  42  52  100  43 
31  0  1  31  1  0  1  45  93  1 
32  9  5  2  16  42  31  48  100  43 
33  2  3  3  11  14  15  45  100  24 
34  2  3  2  17  19  20  47  100  44 
35  2  3  5  7  12  13  48  100  5 
36  10  8  2  18  65  55  54  100  44 
37  0  1  37  1  0  1  45  94  1 
38  2  3  2  19  21  22  45  100  44 
39  2  3  3  13  16  17  46  100  25 
40  8  7  2  20  53  50  51  100  45 
41  0  1  41  1  0  1  47  95  1 
42  6  7  2  21  53  54  51  100  45 
43  0  1  43  1  0  1  46  95  1 
44  5  5  2  22  41  40  49  100  45 
45  5  5  3  15  35  33  47  100  26 
46  2  3  2  23  25  26  47  100  45 
47  0  1  47  1  0  1  47  95  1 
48  12  9  2  24  85  76  53  100  45 
49  2  2  7  7  14  8  48  100  0 
50  5  5  2  25  47  43  49  100  46 
Now we may start working with the data, let's for example notice we can make a nice tree of the numbers by assigning each number as its parent its greatest divisor:
1

....'...........
              
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 < primes
        
 .'. .+. ..'.. .'. .'.   
                
4 6 9 10 15 25 14 21 35 49 22 33 26 39 34 38 46
        
  .'.  .'.    
          
8 12 18 27 20 30 45 50 28 42 44
   
16 24 36 40
 
32 48
Here patterns start to show, for example the level one of the tree are all prime numbers. Also in this tree we can nicely find the greatest common divisor of two numbers as their closest common ancestor. Also if we go from low numbers to high numbers (1, 2, 3, ...) we see we go kind of in a zigzag direction around the bottomright diagonal  what if we make a program that plots this path? Will we see something interesting? We could use this tree to encode numbers in an alternative way too, by indicating path to the number, for example 45 = {2,1,1}. Would this be good for anything? If we write numbers like this, will some operations maybe become easier to perform? You can just keep diving down rabbit holes like this.
There are different types of numbers, in mathematics we classify them into sets (if we further also consider the operations we can perform with numbers we also sort them into algebras and structures like groups, fields or rings). Though we can talk about finite sets of numbers perfectly well (e.g. modulo arithmetic, Boolean algebra etc.), we are firstly considering infinite sets (curiously some of these infinite sets can still be considered "bigger" than other infinite sets, e.g. by certain logic there is more real numbers than rational numbers, i.e. "fractions"). Some of these sets are subsets of others, some overlap and so forth. Here are some notable number sets (note that a list can potentially not capture all relationships between the sets):
One of the most interesting and mysterious number sets are the prime numbers, in fact many number theorists dedicate their whole careers solely to them. Primes are the kind of thing that's defined very simply but give rise to a whole universe of mysteries and whys, there are patterns that seem impossible to describe, conjectures that look impossible to prove and so on. Another similar type of numbers are the perfect numbers.
Of course there are countless other number sets, especially those induced by various number sequences and functions of which there are whole encyclopedias. Another possible division is e.g. to cardinal and ordinal numbers: ordinal numbers tell the order while cardinals say the size (cardinality) of a set  when dealing with finite sets the distinction doesn't really have to be made, within natural numbers the order of a number is equal to the size of a set of all numbers up to that number, but with infinite sets this starts to matter  for example we couldn't tell the size of the set of natural numbers by ordinals as there is no last natural number, but we can assign the set a cardinal number (aleph zero)  this gives rise to new kind of numbers.
Worthy of mentioning is also linear algebra which treats vectors and matrices like elementary algebra treats numbers  though vectors and matrices aren't usually seen as numbers, they may be seen as an extension of the concept.
Numbers are awesome, just ask any number theorist (or watch a numberphile video for that matter). Normal people see numbers just as boring soulless quantities but the opposite is true for that who studies them  study of numbers goes extremely deep, possibly as deep as humans can go and once you get a closer look at something, you discover the art of nature. Each number has its own unique set of properties which give it a kind of "personality", different sets of numbers create species and "teams" of numbers. Numbers are intertwined in intricate ways, there are literally infinitely many patterns that are all related in weird ways  normies think that mathematicians know basically everything about numbers, but in higher math it's the exact opposite, most things about number sequences are mysterious and mathematicians don't even have any clue about why they're so, many things are probably even unknowable. Numbers are also self referencing which leads to new and new patterns appearing without end  for example prime numbers are interesting numbers, but you may start counting them and a number that counts numbers is itself a number, you are getting new numbers just by looking at other numbers. The world of numbers is like a whole universe you can explore just in your head, anywhere you go, it's almost like the best, most free video game of all time, embedded right in this Universe, in logic itself. Numbers are like animals, some are small, some big, some are hardly visible, trying to hide, some can't be overlooked  they inhabit various areas and interact with each other, just exploring this can make you quite happy. { Pokemonlike game with numbers when? ~drummyfish }
There is a famous encyclopedia of integer sequences at https://oeis.org/, made by number theorists  it's quite minimalist, now also free licensed (used to be proprietary, they seem to enjoy license hopping). At the moment it contains more than 370000 sequences; by browsing it you can get a glimpse of how deep the study of numbers goes. These people are also funny, they give numbers entertaining names like happy numbers (adding its squared digits eventually gives 1), polite numbers, friendly numbers, cake numbers, lucky numbers or weird numbers.
Some numbers cannot be computed, i.e. there exist noncomputable numbers. This follows from the existence of noncomputable functions (such as that representing the halting problem). For example let's say we have a real number x, written in binary as 0. d0 d1 d2 d3 ..., where dn is nth digit (1 or 0) after the radix point. We can define the number so that dn is 1 if and only if a Turing machine represented by number n halts. Number x is noncomputable because to compute the digits to any arbitrary precision would require being able to solve the unsolvable halting problem.
All natural numbers are interesting: there is a fun proof by contradiction of this. Suppose there exists a set of uninteresting numbers which is a subset of natural numbers; then the smallest of these numbers is interesting by being the smallest uninteresting number  we've arrived at contradiction, therefore a set of uninteresting numbers cannot exist.
TODO: what is the best number? maybe top 10? would 10 be in top 10? what's the first number that's in top itself?
While mathematicians work mostly with infinite number sets and all kind of "weird" hypothetical numbers like hyperreals and transcendentals, programmers still mostly work with "normal", practical numbers and have to limit themselves to finite number sets because, of course, computers have limited memory and can only store limited number of numeric values  computers typically work with modulo arithmetic with some high power of two modulo, e.g. 2^32 or 2^64, which is a good enough approximation of an infinite number set. Mathematicians are as precise with numbers as possible as they're interested in structures and patterns that numbers form, programmers just want to use numbers to solve problems, so they mostly use approximations where they can  for example programmers normally approximate real numbers with floating point numbers that are really just a subset of rational numbers. This isn't really a problem though, computers can comfortably work with numbers large and precise enough for solving any practical problem  a slight annoyance is that one has to be careful about such things as underflows and overflows (i.e. a value wrapping around from lowest to highest value and vice versa), limited and sometimes nonuniform precision resulting in error accumulation, unlinearization of linear systems and so on. Programmers also don't care about strictly respecting some properties that certain number sets must mathematically have, for example integers along with addition are mathematically a group, however signed integers in two's complement aren't a group because the lowest value doesn't have an inverse element (e.g. on 8 bits the lowest value is 128 and highest 127, the lowest value is missing its partner). Programmers also allow "special" values to be parts of their number sets, especially e.g. with the common IEEE floating point types we see values like plus/minus infinity, negative zero or NaN ("not a number") which also break some mathematical properties and creates situations like having a number that says it's not a number, but again this really doesn't play much of a role in practical problems. Numbers in computers are represented in binary and programmers themselves often prefer to write numbers in binary, hexadecimal or octal representation  they also often meet powers of two rather than powers of ten or primes or other similar limits (for example the data type limits are typically limited by some power of two). There also comes up the question of specific number encoding, for example direct representation, signmagnitude, two's complement, endianness and so on. Famously programmers start counting from 0 (they go as far as using the term "zeroth") while mathematicians rather tend to start at 1. Just as mathematicians have different sets of numbers, programmers have an analogy in numeric data types  a data type defines a set of values and operations that can be performed with them. The following are some of the common data types and representations of numbers in computers:
Here is a table of some notable numbers, mostly important in math and programming but also some famous ones from physics and popular culture (note: the order is rougly from lower numbers to higher ones, however not all of these numbers can be compared easily or at all, so the ordering isn't strictly correct).
number  value  equal to  notes 

minus infinity  not always considered a number, smallest possible value  
minus/negative one  1  i^2, j^2, k^2  
"negative zero"  "0"  zero  nonmathematical, sometimes used in programming 
zero  0  negative zero, e^(i * pi) + 1  "nothing" 
epsilon  1 / omega  infinitesimal, "infinitely small" nonzero  
4.940656... * 10^324  smallest number storable in IEEE754 64 binary float  
1.401298... * 10^45  smallest number storable in IEEE754 32 binary float  
1.616255... * 10^35  Planck length in meters, smallest "length" in Universe  
one eight  0.125  2^3  
one fourth  0.25  2^2  
one third  0.333333...  ...1313132 (5adic)  
one half  0.5  2^1  
one  1  2^0, 0!, 0.999...  NOT a prime 
square root of two  1.414213...  2^(1/2)  irrational, diagonal of unit square, important in geom. 
supergolden ratio  1.465571...  solve(x^3  x^2  1 = 0)  similar to golden ratio, bit more difficult to compute 
phi (golden ratio)  1.618033...  (1 + sqrt(5)) / 2, solve(x^2  x  1 = 0)  irrational, visually pleasant ratio, divine proportion 
two  2  2^1, 0b000010  prime 
silver ratio  2.414213...  1 + sqrt(2), solve(x^2  2 * x  1 = 0)  similar to golden ratio 
e (Euler's number)  2.718281...  base of natural logarithm  
three  3  2^2  1  prime, max. unsigned number with 2 bits 
pi  3.141592...  circle circumference to its diameter, irrational  
four  4  2^2, 0b000100  first composite number 
five  5  (twin) prime, number of platonic solids  
six  6  3!, 1 * 2 * 3, 1 + 2 + 3  highly composite number, perfect number 
tau  6.283185...  2 * pi  radians in full circle, defined mostly for convenience 
thrembo  ???  the hidden number  
seven  7  2^3  1  (twin) prime, days in week, max. unsigned n. with 3 bits 
eight  8  2^3, 0b001000  
nine  9  
ten  10  10^1, 1 + 2 + 3 + 4  your IQ? :D 
twelve, dozen  12  2 * 2 * 3  highly composite number 
fifteen  15  2^4  1, 0b1111, 0x0f, 1 + 2 + 3 + 4 + 5  maximum unsigned number storable with 4 bits 
sixteen  16  2^4, 2^2^2, 0b010000  
twenty four  24  2 * 2 * 2 * 3, 4!  highly composite number 
thirty one  31  2^5  1  maximum unsigned number storable with 5 bits 
thirty two  32  2^5, 0b100000  
thirty six  36  2 * 2 * 3 * 3  highly composite number 
thirty seven  37  most commonly chosen 1 to 100 "random" number  
fourty two  42  cringe number, answer to some stuff  
fourty eight  48  2^5 + 2^4, 2 * 2 * 2 * 2 * 3  highly composite number 
sixty three  63  2^6  1  maximum unsigned number storable with 6 bits 
sixty four  64  2^6  
sixty nine  69  sexual position  
ninety six  96  2^5 + 2^6  
one hundred  100  10^2  
one hundred twenty one  121  11^2  
one hundred twenty seven  127  2^7  1  maximum value of signed byte 
one hundred twenty eight  128  2^7  
one hundred fourty four  144  12^2  
one hundred sixty eight  168  24 * 7  hours in week 
two hundred fifty five  255  2^8  1, 0b11111111, 0xff  maximum value of unsigned byte 
two hundred fifty six  256  2^8, 16^2, ((2^2)^2)^2  number of values that can be stored in one byte 
three hundred sixty  360  2 * 2 * 2 * 3 * 3 * 5  highly composite number, degrees in full circle 
four hundred twenty  420  some stoner shit (they like to smoke it at 4:20)  
five hundred twelve  512  2^9  
six hundred and sixty six  666  number of the beast  
one thousand  1000  10^3  
one thousand twenty found  1024  2^10  
two thousand fourty eight  2048  2^11  
four thousand ninety six  4096  2^12  
ten thousand  10000  10^4, 100^2  
... (enough lol)  65535  2^16  1  maximum unsigned number storable with 16 bits 
65536  2^16, 256^2, 2^(2^(2^2))  number of values storable with 16 bits  
80085  looks like BOOBS  
hundred thousand  100000  10^5  
one million  1000000  10^6  
one billion  1000000000  10^9  
3735928559  0xdeadbeef  one of famous hexadeciaml constants, spells out DEADBEEF  
4294967295  2^32  1, 0xffffffff  maximum unsigned number storable with 32 bits  
4294967296  2^32  number of values storable with 32 bits  
one trillion  1000000000000  10^12  
18446744073709551615  2^64  1  maximum unsigned number storable with 64 bits  
18446744073709551616  2^64  number of values storable with 64 bits  
3.402823... * 10^38  largest number storable in IEEE754 32 binary float  
10^80  approx. number of atoms in observable universe  
googol  10^100  often used big number  
asankhyeya  10^140  religious number, often used in Buddhism  
4.65... * 10^185  approx. number of Planck volumes in observable universe  
1.797693... * 10^308  largest number storable in IEEE754 64 binary float  
googolplex  10^(10^100)  10^googol  another large number, number of genders in 21st century 
Graham's number  g64  extremely, unimaginably large number, > googolplex  
TREE(3)  unknown  yet even larger number, > Graham's number  
infinity  not always considered a number, largest possible value  
aleph zero  beth zero, cardinality(N)  infinite cardinal number, "size" of the set of nat. num.  
i (imaginary unit)  j * k  part of complex numbers and quaternions  
j  k * i  one of quaternion units  
k  i * j  one of quaternion units 
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