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 A115215 #11 May 01 2013 19:33:36 %S A115215 1,1,3,2,1,3,6,2,5,4,1,3,6,10,2,5,9,4,8,7,1,3,6,10,15,2,5,9,14,4,8,13, %T A115215 7,12,11,1,3,6,10,15,21,2,5,9,14,20,4,5,8,13,19,7,12,18,11,17,16,1,3, %U A115215 6,10,15,21,28,2,5,9,14,20,27,4,8,13,19,26,7,12,18,25,11,17,24,16,23,22 %N A115215 Sequence obtained by reading the triangles shown below by diagonals. %e A115215 1 %e A115215 1 %e A115215 2 3 %e A115215 1 %e A115215 2 3 %e A115215 4 5 6 %e A115215 1 %e A115215 2 3 %e A115215 4 5 6 %e A115215 7 8 9 10 %e A115215 1 %e A115215 2 3 %e A115215 4 5 6 %e A115215 7 8 9 10 %e A115215 11 12 13 14 15 %Y A115215 See A124171 for another version. %K A115215 nonn %O A115215 1,3 %A A115215 _Colm Mulcahy_, Dec 05 2006 %E A115215 More terms from Jonathan R. Love (japanada11(AT)yahoo.ca), Mar 07 2007