-1 is an odd number.

-1 is a Harshad number, which means it is divisible by the sum of its digits (1 = 1, and -1 is divisible by 1).

In binary, -1 is represented as 1111111111111111111111111111111111111111111111111111111111111111.

In hex, -1 is represented as ffffffffffffffff.