This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A031939 #14 Aug 26 2015 01:34:11 %S A031939 907,1657,3109,3433,3967,5737,5923,6007,6823,7669,8263,8563,8803,8887, %T A031939 9277,10243,10453,10687,11047,11113,11197,11467,11617,11677,11887, %U A031939 12007,13147,13441,13669,14107,14197,15493,16963,17539,17827 %N A031939 Upper prime of a difference of 20 between consecutive primes. %H A031939 <a href="/index/Pri#gaps">Index entries for primes, gaps between</a> %F A031939 a(n) = A031938(n)+20. %t A031939 Prime[Select[Range[2, 5000], Prime[ # ] - Prime[ # - 1] == 20 &]] (* _Stefan Steinerberger_, May 14 2006 *) %Y A031939 Cf. A031937. %K A031939 nonn %O A031939 1,1 %A A031939 _Jeff Burch_