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 A209887 #6 Mar 30 2012 17:30:05 %S A209887 4,5,9,10,11,15,16,20,21,22,26,27,33,34,38,39,40,44,45,49,50,51,55,56, %T A209887 60,61,62,66,67,73,74,78,79,80,84,85,89,90,91,95,96,100,101,102,106, %U A209887 107,108,112,113,117,118,119,123,124,128,129,130,134,135,139,140 %N A209887 Numbers such that A172470(n) = 61. %Y A209887 Cf. A172470. %K A209887 nonn %O A209887 1,1 %A A209887 _Stephen Crowley_, Mar 14 2012