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 A047166 #8 Apr 11 2021 22:15:35
%S A047166 0,0,0,0,1,3,12,24,60,100,205,315,630,980,2156,3528,8260,13692,31620,
%T A047166 51600,115995,186945,418825,675675,1535391,2492919,5728086,9324406,
%U A047166 21448791,34860553,80006668,129804808,298009048,483483128,1113181012,1807560972,4172914197
%N A047166 Number of nonempty subsets of {1,2,...,n} in which exactly 2/5 of the elements are <= n/2.
%H A047166 Andrew Howroyd, <a href="/A047166/b047166.txt">Table of n, a(n) for n = 1..500</a>
%F A047166 a(n) = Sum_{k>=1} binomial(floor(n/2), 2*k)*binomial(ceiling(n/2), 3*k). - _Andrew Howroyd_, Apr 11 2021
%o A047166 (PARI) a(n) = {my(m=n\2); sum(k=1, (n-m)\3, binomial(m, 2*k)*binomial(n-m, 3*k))} \\ _Andrew Howroyd_, Apr 11 2021
%Y A047166 Cf. A047165.
%K A047166 nonn
%O A047166 1,6
%A A047166 _Clark Kimberling_
%E A047166 Terms a(35) and beyond from _Andrew Howroyd_, Apr 11 2021