The nth term of a geometric sequence is a × rⁿ⁻¹. First term 2 and ratio 3: the 5th term is 2 × 3⁴ = 162. Sequences as a set are in geometric sequences.
Exponent is n minus one
Five terms means four multiplications by r. The sum of those terms is a different leftover, in geometric series sum.
The short list is in ACT Math formulas.
The bottom line
aₙ = arⁿ⁻¹. The exponent is one less than the term number.
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