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 A215252 #11 Sep 14 2012 21:52:37 %S A215252 0,1,1,3,12,56,289,1602,9367,57075,359346,2323416,15356446,103389175, %T A215252 707107627,4901988047,34384943850,243694702311,1742953208739, %U A215252 12567593026554,91280392585747,667341975412356,4907899368783645,36289929612761691,269660272111724536,2012845416966620068,15087243969226496324,113521159338891300347,857211201390859034536 %N A215252 Number of indecomposable permutations sortable using two parallel stacks. %C A215252 Suggested by _Peter Doyle_ in an email message, Sep 04 2012 %H A215252 N. J. A. Sloane, <a href="/A215252/b215252.txt">Table of n, a(n) for n = 0..100</a> %F A215252 INVERTi transform of A216040. %Y A215252 Cf. A003319, A216040, A182216, A215257. %K A215252 nonn %O A215252 0,4 %A A215252 _N. J. A. Sloane_, Sep 07 2012. a(0)=0 added by _N. J. A. Sloane_, Sep 12 2012