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 A126158 #5 Sep 08 2013 13:31:00 %S A126158 1,35,1195,63365,5126905,594825635,93900238195,19371302880965, %T A126158 5061231946045105,1633629246059544035,638388562675692767995, %U A126158 297033561831219312442565,162266449500902451982091305 %N A126158 Secondary diagonal of symmetric triangle A126155: a(n) = A126155(n+1,n). %F A126158 a(n)=A126157(n+1)-4*A126157(n). - _Philippe Deléham_, Jul 22 2007 %Y A126158 Cf. A126155; A126156 (column 0), A126157 (main diagonal). %K A126158 nonn %O A126158 0,2 %A A126158 _Paul D. Hanna_, Dec 20 2006