find the n th term and sum to n terms of the series:1+(1+2)+(1+2+2^2)+.....
since sum(k=0..n) 2^k = 2^n - 1 your series is
1 + 3 + 7 + 15 + ...
= (2-1)+(4-1)+(8-1)+...
= sum(k=1..n) 2^k - n
see where that takes you
1 + 3 + 7 + 15 + ...
= (2-1)+(4-1)+(8-1)+...
= sum(k=1..n) 2^k - n
see where that takes you