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 A215257 #18 Dec 15 2013 17:18:23 %S A215257 0,1,1,3,13,67,383,2345,15069,100341,686515,4797997,34110765, %T A215257 245926667,1793867881,13214905229,98177212059,734746226575, %U A215257 5534054981071,41917876423855,319102504087883,2440086947417629,18733909260242195,144354928765952131,1116015033661158079,8654019249571514621,67292250859412467583,524583875375437922949 %N A215257 Number of indecomposable permutations sortable by a double-ended queue. %C A215257 Suggested by _Peter Doyle_ in an email message, Sep 04 2012 %H A215257 N. J. A. Sloane, <a href="/A215257/b215257.txt">Table of n, a(n) for n = 0..100</a> %F A215257 INVERTi transform of A182216. %Y A215257 Cf. A003319, A182216, A216040, A215252. %K A215257 nonn %O A215257 0,4 %A A215257 _N. J. A. Sloane_, Sep 07 2012. a(0)=0 added by _N. J. A. Sloane_, Sep 12 2012 %E A215257 Name clarified by _Peter Doyle_, Dec 13 2013