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%I #13 Jun 10 2019 00:24:46
%S 0,0,0,0,0,0,0,0,0,0,0,8,9,10,50,55,60,180,195,210,490,525,560,1240,
%T 1326,1413,3645,3933,4230,12750,13860,15015,45375,49335,53460,150524,
%U 163175,176345,470665,509067,549094,1461278,1580761
%N Number of nonempty subsets of {1,2,...,n} in which exactly 4/5 of the elements are <= n/3.
%H Robert Israel, <a href="/A048000/b048000.txt">Table of n, a(n) for n = 1..5711</a>
%F a(n) = Sum_{k=1..floor(n/5)} binomial(floor(n/3), 4*k)*binomial(ceiling(2*n/3), k). - _Robert Israel_, Feb 05 2017
%p f:= proc(n) local k;
%p add(binomial(floor(n/3),4*k/5)*binomial(n-floor(n/3),k/5),k=5..n,5)
%p end proc:
%p map(f, [$1..60]); # _Robert Israel_, Feb 05 2017
%o (PARI) a(n)=sum(k=1,n\5, binomial(n\3, 4*k)*binomial(ceil(2*n/3),k)) \\ _Charles R Greathouse IV_, Feb 05 2017
%K nonn
%O 1,12
%A _Clark Kimberling_
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