reb0rn

Description soda has a set  with  integers . A set is called key set if the sum of integers in the set is an even number. He wants to know how many nonempty subsets of  are key set.

Description People are different. Some secretly read magazines full of interesting girls' pictures, others create an A-bomb in their cellar, others like using Windows, and some like difficult mat

Description Fermat's theorem states that for any prime number p and for any integer a > 1, ap = a (mod p). That is, if we raise a to the pth power and divide by p, the remainder is a. Some (but