If N denotes the set of all positive integers and if : `NtoN` is defined by f(n)= the sum of positive divisors of n, then `f(2^(k).3)`, where k is a positive integer, is

Options

A. `2^(k+1)-1`
B. `2(2^(k+1)-1)`
C. `3(2^(k+1)-1)`
D. `4(2^(k+1)-1)`

Answer

D