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 A049833 #10 Aug 08 2021 03:45:17 %S A049833 0,1,5,13,23,40,54,80,104,131,161,209,231,288,332,376,426,499,549,631, %T A049833 673,748,826,940,972,1073,1177,1261,1347,1490,1526,1688,1774,1899, %U A049833 2031,2133,2219,2398,2538,2680,2766,2981,3039,3281,3379,3516,3724,3950,4002 %N A049833 a(n) = T(2n-1,n) + T(2n,n+1) + ... + T(3n-3,2n-2) = sum over a period of n-th diagonal of array T given by A049828. %Y A049833 Cf. A049828. %K A049833 nonn %O A049833 1,3 %A A049833 _Clark Kimberling_ %E A049833 More terms from _Sean A. Irvine_, Aug 07 2021