Question

Identify the recursive formula for the following sequence:
8, 26, 80, 242, . . .

an = an – 1 + 18 where a1 = 8

an = 3an – 1 + 2 where a1 = 8

an = 4an – 1 – 6 where a1 = 242

an = 8 + (n–1) · 18 where a1 = 18

Answer 1

Correct choice: an = 3an–1 + 2 with a1 = 8.

Check:
- a1 = 8
- a2 = 3·8 + 2 = 26
- a3 = 3·26 + 2 = 80
- a4 = 3·80 + 2 = 242

The other options produce arithmetic terms or wrong initial value and do not match the given sequence.