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

%I #5 Mar 30 2012 18:56:54

%S 0,0,0,0,1,4,12,30,60,121,217,364,700,1260,2250,4960,9460,17380,38500,

%T 71071,126763,276549,503685,898380,2006508,3681588,6619596,14981556,

%U 27412041,49146654,111406614,202871284,363087604,828004144

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

%K nonn

%O 1,6

%A _Clark Kimberling_