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 A131231 #4 Feb 26 2022 00:34:57
%S A131231 1,6,1,7,3,1,12,1,3,1,13,3,1,3,1,18,1,3,1,3,1,19,3,1,3,1,3,1,24,1,3,1,
%T A131231 3,1,3,1,25,3,1,3,1,3,1,3,1
%N A131231 3*A130296 - 2*A128174.
%C A131231 Left column = A047225, numbers congruent to {0,1} mod 6: (1, 6, 7, 12, 13, 18, 19, ...).
%C A131231 Row sums = A131229, numbers congruent to {1,7} mod 10: (1, 7, 11, 17, ...).
%F A131231 3*A130296 - 2*A128174 as infinite lower triangular matrices.
%e A131231 First few rows of the triangle:
%e A131231 1;
%e A131231 6, 1;
%e A131231 7, 3, 1;
%e A131231 12, 1, 3, 1;
%e A131231 13, 3, 1, 3, 1;
%e A131231 ...
%Y A131231 Cf. A131229, A047225, A130296, A128174.
%K A131231 nonn,tabl
%O A131231 1,2
%A A131231 _Gary W. Adamson_, Jun 20 2007