2

2 (two) is a positive integer following 1 and preceding 3. Its ordinal form is written "second" or "2nd".
== Properties ==
*2 is , and a — the only number with both of those properties. (An old joke states that this makes 2 the oddest prime of all.)
*Since 10 is a multiple of 2, a number written in base 10 can be easily be tested for evenness by looking at the last decimal digit. Even numbers always end in 0, 2, 4, 6, or 8.
*2 is the smallest .
*Base two, , is used as the basis of modern computing.
*2 is the first superior highly composite number, despite being a prime.
*2 is a degenerate number. See 4 for more info
== In googology ==
*Calling any standard hyperoperation (addition, multiplication, exponentiation, tetration, etc.) with 2 as both of its arguments will always result in 4. BEAF arrays using 2 as a base tend to become degenerate and evaluate to 4: {2, 2 (1) 2} = {2, 2} = = 4. For this reason, Bowers often coins googologisms based on the number 3, which do not become degenerate.
*In Greek-based number naming systems, 2 is associated with prefix di-, and with prefix duo- in Latin systems.
*2 can be named boogaone with the booga- prefix, since booga(1) = 1 + 1 = 2.
*Using Sbiis Saibian's naming system, this number is called clover mite-crumb.4.3.2 - Hyper-E Numbers - Large Numbers
*Aarex Tiaokhiao coined the name binary-uoonol for this number.Part 1 (LAN) - Aarex Googology
*Username5243 coined the name Binary-Goonol for this number, and it's equal to 2[1]1 in Username5243's Array Notation.Part 1 - My Large Numbers
*Licorneuhh coined the names Heads-Unprimol and Tails-Unprimol for this number, equal to R(1) and Я(1) using Primarial Functions. Licorneuhh's numbers site | Numbers (retrieved at 22:24 UTC 18/12/2020).
*HaydenTheGoogologist2009 coined the name Keep the change! for this number, and it's the 1st number in Meet yourself in 105 degrees Celsius.Hayden's Big Numbers - Meet yourself in 105 degrees Celsius. Retrieved 2023-01-12.
=== Googological functions returning 2 ===
*Simple subcubic graph numbers: \(\text{SSCG}(0) = 2\)
*Xi function: \(\Xi(2)=2\)
*Laver table: \(q(1)=2\)
*Exploding Tree function: \(E(2)=2\)
*Latin square: \(L(2)=2\)
*Weak tree function: \(\text{tree}(1)=2\)
*Fast-growing hierarchy: \(f_\alpha(1) = 2\) for any countable ordinal \(\alpha\) equipped with a system of fundamental sequences
*Primarial functions: R(1) = Я(1) = 2
== As a cash denomination ==
Some currencies, such as the and the , have banknotes with this number in the denomination.
Some currencies, such as the , the and the , have coins with this number in the denomination.
== Sources ==
== See also ==
es:2
cs:2
Category:Numbers
Category:Banknote denominations
Category:Class 0
Category:Coin denominations
Category:Factorial numbers
Category:Fibonacci numbers
Category:Numbers 0-99
Category:Palindromic prime numbers
 
Category:Prime numbers
Category:Primorial numbers
Category:Booga-
Category:Googol Regiment
Category:Doogol Regiment
Category:Even numbers