Sum of all Divisors

A number n is said to be 'perfect' if the sum of all its divisors excluding n 'itself' is equal to n. An example of perfect number is :

If N=2^(n-1).(2^n-1) where 2^n-1 is a prime, then the sum of the all divisors of N is

If N=2^(n-1)*(2^(n)-1) where 2^(n)-1 is a prime,then the sum of the all divisors of N is

A number n is said to be perfect if the sum of all its divisors (excluding n itself) is equal to n. An example of perfect number is (a) 6 (b) 9 (c) 15 (d) 21