3

is the integer between and.

Math features

 * 3 is an odd number.
 * 3 is a prime number, so it is a deficient number.
 * 3 is the only number to be both a Mersenne prime and a Fermat prime.
 * 3 is a Mersenne prime, equal to $$2^2-1$$.
 * 3 is a Fermat prime, equal to $$2^{2^0}+1$$.