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 A133728 #14 Aug 16 2025 07:05:19 %S A133728 1,0,3,1,0,5,0,3,0,7,1,0,5,0,9,0,3,0,7,0,11,1,0,5,0,9,0,13,0,3,0,7,0, %T A133728 11,0,15,1,0,5,0,9,0,13,0,17,0,3,0,7,0,11,0,15,0,19,1,0,5,0,9,0,13,0, %U A133728 17,0,21,0,3,0,7,0,11,0,15,0,19,0,23 %N A133728 A128174 * A127775. %C A133728 Row sums are the triangular numbers 1, 3, 6, 10, 15, 21, 28, ...; see A000217. %F A133728 A128174 * A127775 as infinite lower triangular matrices. Triangle by columns: (2k-1, 0, 2k-1, 0, ...) in k-th column. %e A133728 From _Philippe Deléham_, Oct 28 2011: (Start) %e A133728 Triangle begins: %e A133728 1; %e A133728 0, 3; %e A133728 1, 0, 5; %e A133728 0, 3, 0, 7; %e A133728 1, 0, 5, 0, 9; %e A133728 0, 3, 0, 7, 0, 11; %e A133728 1, 0, 5, 0, 9, 0, 13; ... %e A133728 (End) %Y A133728 Cf. A000217. %K A133728 nonn,tabl %O A133728 1,3 %A A133728 _Gary W. Adamson_, Sep 21 2007 %E A133728 Corrected and extended by _Philippe Deléham_, Oct 28 2011