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 A047165 #8 Apr 11 2021 22:15:29
%S A047165 0,0,0,0,0,0,3,4,20,25,75,90,210,245,511,588,1260,1458,3510,4125,
%T A047165 10725,12705,32835,38830,96382,113399,273273,320411,770315,903175,
%U A047165 2208115,2594540,6451500,7594920,18990768,22366458,55715562,65579982,162488703,191126529
%N A047165 Number of nonempty subsets of {1,2,...,n} in which exactly 1/5 of the elements are <= n/2.
%H A047165 Andrew Howroyd, <a href="/A047165/b047165.txt">Table of n, a(n) for n = 1..500</a>
%F A047165 a(n) = Sum_{k>=1} binomial(floor(n/2), k)*binomial(ceiling(n/2), 4*k). - _Andrew Howroyd_, Apr 11 2021
%o A047165 (PARI) a(n) = {my(m=n\2); sum(k=1, (n-m)\4, binomial(m, k)*binomial(n-m, 4*k))} \\ _Andrew Howroyd_, Apr 11 2021
%Y A047165 Cf. A047161, A047166, A047167, A047168.
%K A047165 nonn
%O A047165 1,7
%A A047165 _Clark Kimberling_
%E A047165 Terms a(35) and beyond from _Andrew Howroyd_, Apr 11 2021