This article is from the Puzzles FAQ,
by Chris Cole email@example.com and Matthew Daly
firstname.lastname@example.org with numerous contributions by others.
11 Sequence puzzles (Frequently Asked Puzzles - general)
O, T, T, F, F, S, ? ==> series.06 <== [series]
5, 6, 5, 6, 5, 5, 7, 6, ? ==> series.21 <== [series]
11, 21, 1211, 111221, ? ==> series.07 <== [series]
The problem with letter sequences is that we've seen most of them, quite
possibly even that one you just thought of yourself. Check out the
archive, in the general category "series", to make sure yours isn't there.
The problem with number sequences is that there are infinitely many
formulas that will fit any finite sequence, and the concept of the most
"natural" formula is a subjective one. Since number sequences always lead
to this same discussion, it's best to avoid them in rec.puzzles.
A great service for tracking down number sequences is N.J.A. Sloane's
On-Line Encyclopedia of Integer Sequences. Visit them on the Web at
information on the e-mail server, send a blank message to
The next term in the third series is 312211, since the previous term was
"three 1's, two 2's, one 1".