OEIS

2023-07-10

The Online Encyclopedia of Integer Sequences is a website created by N. J. A. Sloane. The site hosts a database of thousands (363,821 as of the time of this post) of, you guessed it, integer sequences. These sequences are submitted by the public and then reviewed before they make it onto the encyclopedia. The search functionality allows you to search for any integer sequence based on the sequence itself, a keyword, or even a single number in the sequence and each sequence has a unique identification string. Given a sequence, the OEIS displays information regarding the meaning of the sequence, the elements of the sequence, other sequences that are related, and even a formula for the nth term in the sequence if possible.

In a paper published in June 2011, a group of researchers used the vast amount of data in the OEIS to gauge the popularity of specific numbers based on the number of times it appears in the encyclopedia. This creates the above graph (notice the logarithmic scale). The paper noted the noticeable gap that separates groups of numbers and coined the term Sloan's Gap to refer to it. It shows the distinction between the "popular" numbers and the "unpopular" numbers.