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 A133091 #14 Mar 07 2022 00:08:02
%S A133091 1,2,2,1,2,3,2,4,6,4,1,2,3,4,5,2,4,6,8,10,6,1,2,3,4,5,6,7,2,4,6,8,10,
%T A133091 12,14,8,1,2,3,4,5,6,7,8,9,2,4,6,8,10,12,14,16,18,10,1,2,3,4,5,6,7,8,
%U A133091 9,10,11,2
%N A133091 A133080 * A002260.
%C A133091 Row sums = A133092: (1, 4, 6, 16, 15, 36, 28, ...).
%H A133091 G. C. Greubel, <a href="/A133091/b133091.txt">Table of n, a(n) for the first 50 rows, flattened</a>
%F A133091 A133080 * A002260 as infinite lower triangular matrices.
%F A133091 Odd n rows = (1,2,3,...,n). Even n rows = (2,4,6,...,n).
%e A133091 First few rows of the triangle:
%e A133091 1;
%e A133091 2, 2;
%e A133091 1, 2, 3;
%e A133091 2, 4, 6, 4;
%e A133091 1, 2, 3, 4, 5;
%e A133091 2, 4, 6, 8, 10, 6;
%e A133091 1, 2, 3, 4, 5, 6, 7;
%e A133091 ...
%t A133091 T[n_, n_] := n; T[n_, k_] := (2 - (1 - (-1)^n)/2)*k; Table[T[n, k], {n, 1, 10}, {k, 1, n}] (* _G. C. Greubel_, Oct 21 2017 *)
%o A133091 (PARI) for(n=1,10, for(k=1,n, print1(if(k==n, n,(2 - (1 - (-1)^n)/2)*k), ", "))) \\ _G. C. Greubel_, Oct 21 2017
%Y A133091 Cf. A133080, A002260, A133092.
%K A133091 nonn,tabl
%O A133091 1,2
%A A133091 _Gary W. Adamson_, Sep 09 2007
%E A133091 Corrected and extended by _Philippe Deléham_, Mar 02 2012