**3** is the second prime number, and the second single digit prime number. 3's prime factors are 1 and 3. It is said to be the first odd prime, because the previous prime number is 2, which is even.

It is also the first Fermat prime and the first Mersenne Prime.

## Proofs

- Therefore it has 2 factors.

## Relationship with other numbers

### The numbers before

- 2 is the first prime number. It is the only
**even**prime number. **1**, the number before 2, is**not**a prime number.

### The numbers after

- The next odd number, 5, is a prime number.
- There are no odd numbers between 3 and 5, and they are two numbers apart. As a result, they are twin primes.

- 7, the odd number following 5, is a prime number.
- 3 and 7 are four numbers apart, therefore, they are cousin primes.

- 9, the odd number following 7, is not a prime number. It is a square number, and the first odd composite number.

## Usage

### General

- Trilogy refers to a set of three works of art that are connected, either as a single work or three individual works.

### Science

- Lithium's atomic number and number of electrons are 3.
- Group three elements also have the valence of +3. Similarly, group five elements have the valence of -3.
- Tritium / hydrogen-3, has a nucleon number of 3.

### Sports

- In basketball, a shot behind the three-point arc is worth three points, unless in the 3x3 variant.
- In baseball, 3 strikes are required for the player to be considered "out", and 3 outs are required for the attacking team to exchange with the opposing team.

### Video Games

- In The Legend of Zelda series, there is a sacred relic called Triforce, which consists of three separate golden triangles.