Any help F(n)=F(n-1)+F(n-2)+F(n-1)*F(n-2)F[0]=a;F[1]=b;any logn solution ?
use the matrix representation, this might helphttp://www.geeksforgeeks.org/program-for-nth-fibonacci-number/
and don't try to calculate the whole series just think about O(1) solution to find the sum