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 A131911 #6 Mar 05 2022 01:47:35
%S A131911 1,4,3,5,2,5,8,1,2,7,9,2,1,2,9,12,1,2,1,2,11,13,2,1,2,1,2,13,16,1,2,1,
%T A131911 2,1,2,15,17,2,1,2,1,2,1,2,17,20,1,2,1,2,1,2,1,2,19
%N A131911 2*A131821 - A128174.
%C A131911 Left column, congruent to {0, 1} mod 4, A042948: (1, 4, 5, 8, 9, 12, 13, 16, ...).
%C A131911 Row sums = A131912: (1, 7, 12, 18, 23, 29, 34, ...).
%F A131911 2*A131821 - A128174 as infinite lower triangular matrices.
%e A131911 First few rows of the triangle:
%e A131911 1;
%e A131911 4, 3;
%e A131911 5, 2, 5;
%e A131911 8, 1, 2, 7;
%e A131911 9, 2, 1, 2, 9;
%e A131911 12, 1, 2, 1, 2, 11;
%e A131911 13, 2, 1, 2, 1, 2, 13;
%e A131911 ...
%Y A131911 Cf. A131821, A128174, A042948, A131912.
%K A131911 nonn,tabl
%O A131911 1,2
%A A131911 _Gary W. Adamson_, Jul 27 2007