%I #8 Apr 11 2021 22:15:35

%S 0,0,0,0,1,3,12,24,60,100,205,315,630,980,2156,3528,8260,13692,31620,

%T 51600,115995,186945,418825,675675,1535391,2492919,5728086,9324406,

%U 21448791,34860553,80006668,129804808,298009048,483483128,1113181012,1807560972,4172914197

%N Number of nonempty subsets of {1,2,...,n} in which exactly 2/5 of the elements are <= n/2.

%H Andrew Howroyd, <a href="/A047166/b047166.txt">Table of n, a(n) for n = 1..500</a>

%F a(n) = Sum_{k>=1} binomial(floor(n/2), 2*k)*binomial(ceiling(n/2), 3*k). - _Andrew Howroyd_, Apr 11 2021

%o (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 Cf. A047165.

%K nonn

%O 1,6

%A _Clark Kimberling_

%E Terms a(35) and beyond from _Andrew Howroyd_, Apr 11 2021