3

Three (3) is a positive integer one more than 2 and one less than 4.

Properties
Three is the 2nd prime number (between 2 and 5). It is the first odd prime.

3 is the second triangular number (between 1 and 6).

Taking the third power of a number is called taking its cube.

Three is the only number to be both a Mersenne prime and a Fermat prime. It is also a Mersenne prime exponent producing the prime 7. The next exponent is 5, the next Fermat prime is 5, and the next Mersenne prime is 7.

3 is in a twin prime pair with 5.

3 is the fourth member of the Fibonacci sequence (between 2 and 5). It is also a Lucas number (between 1 and 4).

Three is the second lucky number, between 1 and 7.

Testing if a number is a multiple of 3 is as easy as adding up the digits and seeing if they add to a multiple of 3. So 59604 is a multiple of 3 since its digits add to 24, which is a multiple of 3.