Continue the series: 3, 17, 55, 129, 251
I've been looking at it for a while and I can't figure it out?
apparently not.
The ratio between terms steadily decreases, so it is not an exponential.
So, it must be some kind of polynomial or logarithmic function. The integer values pretty much rule out logs. So, ...
x^2 grows like: 1,4,9,16,25,... too slow
x^3 grows like: 1,8,27,64,125,... hmmm close.
I see the sequence as
Tn = 2n^3 + 1