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 A128077 #6 Feb 15 2022 02:11:04 %S A128077 1,1,4,1,2,9,1,2,3,16,1,2,3,4,25,1,2,3,4,5,36,1,2,3,4,5,6,49,1,2,3,4, %T A128077 5,6,7,64 %N A128077 A128064 * A002260. %C A128077 Row sums = the pentagonal numbers, A000326: 1, 5, 12, 22, 35, 51, ... %F A128077 A128064 * A002260 as infinite lower triangular matrices. Triangle read by rows, a(1) = 1; n-th row = first (n-1) terms of (1, 2, 3, ...) followed by n^2. %e A128077 First few rows of the triangle: %e A128077 1; %e A128077 1, 4; %e A128077 1, 2, 9; %e A128077 1, 2, 3, 16; %e A128077 1, 2, 3, 4, 25; %e A128077 ... %Y A128077 Cf. A128064, A002260, A000326, A128078. %K A128077 nonn,tabl %O A128077 1,3 %A A128077 _Gary W. Adamson_, Feb 14 2007