Two (2) is a positive integer one more than 1 and one less than 3.

## PropertiesEdit

Two is the 1st prime number (next is 3), and the only even prime number.

Taking the second power of a number is called taking its square.

Two is the base of the binary system, used in computers.

2 is a Mersenne exponent, producing the prime 3. The next exponent is 3.

Powers of two are important in many areas including computer science. The next power of two is 4.

Two is the third member of the Fibonacci sequence (following 1 and preceding 3).

Two is the second factorial number (between 1 and 6), and the first primorial number (next is 6).

2 is the second highly composite number, being the first with 2 or more factors. The next one is 4. It is the only prime highly composite number.

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 Edit

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} = 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.

Using Sbiis Saibian's naming system, this number is called **clover mite-crumb**.^{[1]}

Testing for divisibility by 2 is as simple as checking if the last digit is 0, 2, 4, 6, or 8. If it is, the number is divisible by 2. For instance, 234748 ends in 8 and is a multiple of 2.

"Palpable" numbers are numbers small enough to be recognized immediately. You can fully wrap your mind around 3 (or maybe 6) things, but not in larger numbers like a thousand. In other words, these numbers can be touched or felt (that's what palpable means).

### Googological functions returning 2 Edit

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

## As a cash denomination Edit

Some currencies, such as the Ghanaian cedi and the United States dollar, have banknotes with this number in the denomination.

Some currencies, such as the euro and the pound sterling, have coins with this number in the denomination.