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 A131413 #8 Jun 07 2023 06:21:50 %S A131413 1,4,3,7,6,5,10,9,8,7,13,12,11,10,9,16,15,14,13,12,11,19,18,17,16,15, %T A131413 14,13,22,21,20,19,18,17,16,15,25,24,23,22,21,20,19,18,17,28,27,26,25, %U A131413 24,23,22,21,20,19,31,30,29,28,27,26,25,24,23,22,21,34,33,32,31,30,29,28,27,26,25,24,23 %N A131413 Triangle read by rows: A002024 + A128076 - A000012 as infinite lower triangular matrices. %C A131413 Row sums = A000566, the heptagonal numbers: (1, 7, 18, 34, 55, ...). %F A131413 By rows, (n+1) terms of 3n+1, 3n, 3n-1, ... %e A131413 First few rows of the triangle: %e A131413 1; %e A131413 4, 3; %e A131413 7, 6, 5; %e A131413 10, 9, 8, 7; %e A131413 13, 12, 11, 10, 9; %e A131413 16, 15, 14, 13, 12, 11; %e A131413 19, 18, 17, 16, 15, 14, 13; %e A131413 ... %Y A131413 Cf. A000566, A002024, A128076. %K A131413 nonn,tabl %O A131413 0,2 %A A131413 _Gary W. Adamson_, Jul 08 2007 %E A131413 a(5) = 5, a(30) = 20 corrected and more terms from _Georg Fischer_, Jun 07 2023