-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.