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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =6a(7) =10a(8) =40a(9) =60a(10) =150a(11) =210a(12) =455a(13) =630a(14) =1470a(15) =2142a(16) =5544a(17) =8400a(18) =21630a(19) =32802a(20) =80520a(21) =121110a(22) =290400a(23) =437580a(24) =1056627a(25) =1608607a(26) =3929926a(27) =6034600a(28) =14742910a(29) =22712326