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 A047163 #8 Apr 11 2021 22:15:17
%S A047163 0,0,0,0,2,3,12,16,40,50,110,135,315,392,980,1232,3080,3864,9480,
%T A047163 11850,29040,36300,89870,112519,280423,351351,876603,1098188,2741102,
%U A047163 3433703,8586788,10758608,26965808,33794504,84844280,106344792,267298650,335061789,843098172,1056924666
%N A047163 Number of nonempty subsets of {1,2,...,n} in which exactly 1/4 of the elements are <= n/2.
%H A047163 Andrew Howroyd, <a href="/A047163/b047163.txt">Table of n, a(n) for n = 1..500</a>
%F A047163 a(n) = Sum_{k>=1} binomial(floor(n/2), k)*binomial(ceiling(n/2), 3*k). - _Andrew Howroyd_, Apr 11 2021
%o A047163 (PARI) a(n) = {my(m=n\2); sum(k=1, (n-m)\3, binomial(m, k)*binomial(n-m, 3*k))} \\ _Andrew Howroyd_, Apr 11 2021
%Y A047163 Cf. A047161, A047164.
%K A047163 nonn
%O A047163 1,5
%A A047163 _Clark Kimberling_
%E A047163 Terms a(35) and beyond from _Andrew Howroyd_, Apr 11 2021