The on-line encyclopedia of integer sequences

Abstract

We all recognize 0, 1, 1, 2, 3, 5, 8, 13,... but what about 1, 2, 4, 6, 3, 9, 12, 8, 10, 5, 15,...? If you come across a number sequence and want to know if it has been studied before, there is only one place to look, the On-Line Encyclopedia of Integer Sequences (or OEIS). Now in its 49th year, the OEIS contains over 220,000 sequences and 20,000 new entries are added each year. This article will briefly describe the OEIS and its history. It will also discuss some sequences generated by recurrences that are less familiar than Fibonacci's, due to Greg Back and Mihai Caragiu, Reed Kelly, Jonathan Ayres, Dion Gijswijt, and Jan Ritsema van Eck.