5 (five) is a number, numeral, and glyph. It is the natural number following 4 and preceding 6.

The SI prefix for 10¹⁵ is peta (P), and for its reciprocal femto (f).

Five is between 4 and 6 and is the third prime number, after 2 and 3, and before 7. Because it can be written as 2^(2^1)+1, five is classified as a Fermat prime. 5 is the third Sophie Germain prime, the first safe prime, and the third Mersenne prime exponent. Five is the first Wilson prime and the third factorial prime, also an alternating factorial. It is an Eisenstein prime with no imaginary part and real part of the form $3n\; -\; 1$. It is also the only number that is part of more than one pair of twin primes.

More on Five Points AL, Chambers