If the ratio of each term of a sequence to its previous term from the second term onwards is equal to the same constant, this sequence is called a geometric sequence. This constant is called the common ratio of the geometric sequence, which is usually represented by the letter q (q≠0), and the geometric sequence a1≠0. Note: When q=1, an is a constant sequence.

General formula:a_n = [a₁ q ^(n-1)]

a₁ - First Item

n - number of items

q - common ratio