Math
posted by Neil .
20
(Sigma Sign) 2n + 7
k= 1

∑2n+7
=2∑n + ∑ 7
=2*(20+1)(20/2) + 20*7
=420+140
=560 
Thank you, MathMate.

Wait, do you know how it could be plugged into the Sn= a1 (1  r^n/ 1  r) formula?

Sn= a1 (1  r^n/ 1  r)
applies when the series is a geometric progression, such as
20
∑ a1*r^i
i=1