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 A089841 #5 Mar 31 2012 14:02:17 %S A089841 0,0,0,0,6,0,4,0,0,11,0,9,1653699,1653578,1654426,1654694,1654312, %T A089841 1655572,1654937,1655787,1655152,1654694,0,0,26,0,24,0,0,35,37,43,41, %U A089841 0,40,29,41,0,28,0,34,0,28,31,37,0,0,49,0,47,0,0,58,60,66,64,0,63,52 %N A089841 Main diagonal of A089839. a(n) = A089839(n,n). %C A089841 When a(n) is 0, the corresponding row in A089840 (referred here as A089840[n]) is an involution. %H A089841 A. Karttunen, <a href="/A089839/a089839.c.txt">C-program for computing the initial terms of this sequence</a> %K A089841 nonn %O A089841 0,5 %A A089841 _Antti Karttunen_, Dec 05 2003