The On-Line Encyclopedia of Integer Sequences

URL:    http://www.research.att.com/~njas/sequences/

 An annotated database of over 80,000 number sequences.
Have you ever needed to know (for example) what comes next after
1, 2, 4, 9, 20, 48, 115, 286, 719, ... ?
This is the place to find the answer!