Thread: geo sequence

1, 2, 4, 8, 16

In the above sequence, the first term is 1 and each term after the first is twice the preceding term. What is the sum of the 16th, 17th, and 18th terms?

I know 2^15 + 2^16 + 2^17 is the sum but how can I express it as 7(2^15)?

Originally Posted by dannyc

1, 2, 4, 8, 16

In the above sequence, the first term is 1 and each term after the first is twice the preceding term. What is the sum of the 16th, 17th, and 18th terms?

I know 2^15 + 2^16 + 2^17 is the sum but how can I express it as 7(2^15)?

Factor out .