5

Five (5) is a positive integer one more than 4 and one less than 6.

Properties
5 is the third prime number (between 3 and 7). It is a Mersenne prime exponent (producing 31), and a Fermat prime (between 3 and 17).

5 is the second square pyramidal number (between 1 and 14), and the second pentatope number (between 1 and 15).

5 is the only number to be twin primes with two numbers. It forms pairs with both 3 and 7.

5 is the fifth term of the Fibonacci sequence, between 3 and 8.

5 is half of 10, our number base, and is the number of fingers on one hand.

Related to this, to test if a number is divisible by 5, all you need to do is check the last digit. If it is 0 or 5, the number is divisible by 5.