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 A230551 #14 Oct 29 2013 11:22:06 %S A230551 1,2,4,10,24,62,154,396,992,2536,6376,16238,40914,103954,262298, %T A230551 665478,1680726,4260262,10766470,27274444 %N A230551 Number of involutions avoiding the pattern 2431. %H A230551 Miklós Bóna, Cheyne Homberger, Jay Pantone, and Vince Vatter, <a href="http://arxiv.org/abs/1310.7003">Pattern-avoiding involutions: exact and asymptotic enumeration</a>, arxiv:1310.7003, 2013. %e A230551 Of the 26 involutions of length 26, only 35142 and 52431 contain the pattern 2431, so a(5) = 24. %Y A230551 Cf. A001006, A121704, A230552-A230556. %K A230551 nonn %O A230551 1,2 %A A230551 _Cheyne Homberger_, Oct 23 2013