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 A134237 #9 Feb 08 2022 20:18:41 %S A134237 1,3,2,5,6,3,7,8,9,4,9,10,11,12,5,11,12,13,14,15,6,13,14,15,16,17,18, %T A134237 7,15,16,17,18,19,20,21,8,17,18,19,20,21,22,23,24,9,19,20,21,22,23,24, %U A134237 25,26,27,10,21,22,23,24,25,26,27,28,29,30,11,23,24,25,26,27,28,29,30,31,32,33,12 %N A134237 Triangle read by rows, a(1) = 1, n-th row n terms of: (2n-1, 2n, 2n+1, ..., followed by n). %C A134237 Row sums = A134238: (1, 5, 14, 28, 47, 71, 100, 134, ...). %e A134237 First few rows of the triangle: %e A134237 1; %e A134237 3, 2; %e A134237 5, 6, 3; %e A134237 7, 8, 9, 4; %e A134237 9, 10, 11, 12, 5; %e A134237 11, 12, 13, 14, 15, 6; %e A134237 13, 14, 15, 16, 17, 18, 7; %e A134237 ... %o A134237 (PARI) T(n, k) = if (k < n, (2*n-1) + (k-1), n); %o A134237 tabl(nn) = for (n=1, nn, for (k=1, n, print1(T(n, k), ", ")); print); \\ _Michel Marcus_, Jul 13 2017 %Y A134237 Cf. A134238. %K A134237 nonn,tabl %O A134237 1,2 %A A134237 _Gary W. Adamson_, Oct 14 2007 %E A134237 Corrected and extended by _Michel Marcus_, Jul 13 2017