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 &mdash; 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 only even prime number.

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.

Using Sbiis Saibian's naming system, this number is called clover mite-crumb.

Aarex Tiaokhiao calls this number binary-uoonol.

Username5243 calls this number Binary-Goonol, and it's equal to 2[1]1 in Username5243's Array Notation.

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: \(\text{tree}(1)=2\)