What is the next number in the series 1 3 11 31 69 -?

2 Answers

Oddman Profile
Oddman answered
First differences are 3-1, 11-3, and so on ...
  2, 8, 20, 38
Second differences are
  6, 12, 18
Each second difference is 6 more than the last. The next second difference will be 18+6 = 24. The next first difference will be 38+24 = 62.

The next number in sequence is probably 69+62 = 131.
thanked the writer.
Richard Scott
Richard Scott commented
There are two sequences that can be used, yours and mine.
Oddman
Oddman commented
I've told you my rule. I haven't seen a description of yours. Without a statement of the rule, *any* number will do.

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