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

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

%S 0,0,0,0,1,3,12,30,60,121,217,385,700,1260,2521,4960,9460,20020,38500,

%T 71071,148161,276549,503685,1071525,2006508,3681588,8013256,14981556,

%U 27412041,60042147,111406614,202871284,447617884,828004144

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

%K nonn

%O 1,6

%A _Clark Kimberling_