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Number of nonempty subsets of {1,2,...,n} in which exactly 1/5 of the elements are <= (n+3)/3.
0

%I #4 Mar 30 2012 18:56:54

%S 0,0,0,0,0,0,3,15,20,60,140,175,360,720,891,1935,4455,5775,13895,

%T 32487,42484,97188,216580,282165,632706,1418514,1863880,4259520,

%U 9690000,12833436,29366007,66481107,88256147,200571107,452679491

%N Number of nonempty subsets of {1,2,...,n} in which exactly 1/5 of the elements are <= (n+3)/3.

%K nonn

%O 1,7

%A _Clark Kimberling_