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 A231621 #7 Apr 27 2017 10:34:41
%S A231621 1,1,2,6,28,189,1873,27201,578949,18059374,825604416,55315679788,
%T A231621 5431645680297,781666575692345,164861247948842305,
%U A231621 50959194632488457965,23085190353310504913320,15326793132326730009566200,14913379277290330452859885202,21267074956884103635776195255433,44447403127130268192387935737712641
%N A231621 a(n) = A000930(n*(n+1)/2), where A000930 is Narayana's cows sequence.
%H A231621 G. C. Greubel, <a href="/A231621/b231621.txt">Table of n, a(n) for n = 0..100</a>
%F A231621 a(n) = [x^(n*(n+1)/2)] 1 / (1 - x - x^3) for n>=0.
%t A231621 Table[SeriesCoefficient[1/(1 - x - x^3), {x, 0, n*(n + 1)/2}], {n,0,50}] (* _G. C. Greubel_, Apr 26 2017 *)
%o A231621 (PARI) {a(n) = polcoeff(1/(1-x-x^3 + x*O(x^(n*(n+1)/2))), n*(n+1)/2)}
%o A231621 for(n=0, 20, print1(a(n), ", "))
%Y A231621 Cf. A000930, A231620.
%K A231621 nonn
%O A231621 0,3
%A A231621 _Paul D. Hanna_, Nov 13 2013