The sum of a geometric sequence, that is, a series a1 + a2 + a3 + ... in which the terms form a geometric sequence.
The sum of the first n terms can be obtained as follows:
|Sn|| = a1 + a2 + a3 + ...an|
| = a1 + a1r + a1r2 + ... + a1rn-1|
| = a1 (rn - 1)/(r - 1)|
in which r is the common ratio.