Geometric progression

Geometric sequence, is a sequence of numbers where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio.
For example: 1, 2, 4,.....,32,64,128,...

a1,a2,a3,...,an1,an,an+1,...

n-th term of the sequence:

an=a1qn1
|an|=an1an+1,  n>1

The sum of the first n terms:

Sn=a1qn1q1,  q1
Keywords: Geometric progression