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 A145221 #32 Apr 22 2016 22:31:20 %S A145221 0,0,1,0,6,20,135,924,7420,66744,667485,7342280,88107426,1145396460, %T A145221 16035550531,240533257860,3848532125880,65425046139824, %U A145221 1177650830516985,22375365779822544,447507315596451070,9397653627525472260,206748379805560389951,4755212735527888968620 %N A145221 Duplicate of A000387. %K A145221 dead %O A145221 0,5