Forty five
45 is an odd number.
45 is a Harshad number, which means it is divisible by the sum of its digits (4 + 5 = 9, and 45 is divisible by 9).
In binary, 45 is represented as 101101.
In hex, 45 is represented as 2d.
Prime factorization of 45: 32 * 5.