Number of nonempty subsets of {1,2,...,n} in which exactly 1/2 of the elements are <= (n-4)/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =5a(6) =6a(7) =27a(8) =35a(9) =119a(10) =164a(11) =494a(12) =714a(13) =2001a(14) =3002a(15) =8007a(16) =12375a(17) =31823a(18) =50387a(19) =125969a(20) =203489a(21) =497419a(22) =817189a(23) =1961255a(24) =3268759a(25) =7726159a(26) =13037894a(27) =30421754a(28) =51895934a(29) =119759849