4 | |||||||||
---|---|---|---|---|---|---|---|---|---|
Numbers 0 - 99 | |||||||||
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 |
20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 |
30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 |
40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 |
50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 |
60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 |
70 | 71 | 72 | 73 | 74 | 75 | 76 | 77 | 78 | 79 |
80 | 81 | 82 | 83 | 84 | 85 | 86 | 87 | 88 | 89 |
90 | 91 | 92 | 93 | 94 | 95 | 96 | 97 | 98 | 99 |
4 (four) is a positive integer following 3 and preceding 5. Its ordinal form is written "4th" or "fourth".

Properties

Visualization of 4
- 4 is a composite number, and the first natural number with this property. 4 is an even square number. 4 is the 2nd tetrahedral number. 4 is the 2nd Busy Beaver number. 4 is the 2nd superperfect number. Plugging 2 into the hyper operators degenerates to 4: \(2 \uparrow\uparrow ... \uparrow\uparrow 2 = 4\).
- 4 is associated with bad luck in Eastern numerology because the Chinese word for "four" sounds similar to the word for "death."
- It is possible to test for divisibility by 4 in base 10 by looking at last 2 digits of the number. If the 2-digit number is divisible by 4, then the whole number is.
- Ignoring weekdays, the Julian calendar repeats every 4 years.
- Its Roman numeral is most commonly IV, but on clock faces, IIII is also used.
- Its prime factorization is 4 = 2².
- All known multiperfect numbers > 6 are divisible by 4.
- Base four, sometimes used as a way of compressing binary, is called quaternary.
In googology
- Some googologisms based on 4 are supertet, quadroogol and googolquadriplex. 4 can be thought as zeroth term of sequence defining Graham's number: \(g_0\) = 4.
- In Greek-based number naming systems, 4 is associated with prefix tetra-, and with prefix quadri- in Latin systems.
- 4 can be named gartwo, fztwo, fugatwo, megafugatwo, or boogatwo with the gar-, fz-, fuga-, megafuga-, and booga- prefixes respectively.
- Aarex Tiaokhiao coined the name binary-booiol or binary-golsol for this number, as s(2,100,1,2) = s(2,2,100,1) = s(2,2,100) in strong array notation.[1]
- Username5243 coined the names Binary-Goodol and Binary-Goonolplex for this number, and it's equal to 2[1]2 = 2[1]2[1]1 in Username5243's Array Notation.[2]
Googological functions returning 4
- Rado's Sigma Function: \(\Sigma(2)=4\)
- Xi function: \(\Xi(4)=4\)
- Hyperfactorial: \(H(2)=4\)
- Factorexation: \(2\,\backslash=4\)
- Superfactorial (Clifford Pickover): \(2\$=4\)
Sources
Gar-: garone · gartwo · garthree · garfour · garfive · garsix · garseven · gareight · garnine · garten · garhundred · gargoogol · gartrialogue · gargoogolplex · gargiggol
Fz-: fzone · fztwo · fzthree · fzfour · fzfive · fzsix · fzseven · fzeight · fznine · fzten · fzeleven · fztwelve · fzthirteen · fzfourteen · fzfifteen · fzsixteen · fzseventeen · fzeighteen · fznineteen · fztwenty · fzthirty · fzforty · fzfifty · fzsixty · fzseventy · fzeighty · fzninety · fzhundred · fzgoogol · fzmillion · fzmilliplexion · fzgoogolplex · fzgargoogolplex · fzgargantugoogolplex · fzgiggol
Fuga-: fugaone · fugatwo · fugathree · fugafour · fugafive · fugasix · fugaseven · fugaeight · fuganine · fugaten · fugaeleven · fugahundred · fugagoogol · fugagoogolplex · fugagargoogolplex · fugagargantugoogolplex · fugagiggol
Megafuga-: megafugaone · megafugatwo · megafugathree · megafugafour · megafugafive · megafugasix · megafugaseven · megafugaeight · megafuganine · megafugaten · megafugaeleven · megafugatwelve · megafugathirteen · megafugafourteen · megafugafifteen · megafugasixteen · megafugaseventeen · megafugaeighteen · megafuganineteen · megafugatwenty · megafugathirty · megafugaforty · megafugafifty · megafugasixty · megafugaseventy · megafugaeighty · megafuganinety · megafugahundred · megafugagoogol · megafugagoogolplex · megafugagargoogolplex · megafugagargantugoogolplex
Booga-: boogaone · boogatwo · boogathree · boogafour · boogafive · boogasix · boogaseven · boogaeight · booganine · boogaten · boogahundred · boogagoogol · boogagoogolplex
Gag: gagone · gagtwo · gagthree · gagfour · gagfive · gagsix · gagseven · gageight · gagnine · gagten · gaghundred · gaggoogol · gaggoogolplex