Number of nonempty subsets of {1,2,...,n} in which exactly 1/6 of the elements are <= (n-2)/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =2a(7) =3a(8) =18a(9) =24a(10) =84a(11) =105a(12) =280a(13) =336a(14) =756a(15) =882a(16) =1785a(17) =2044a(18) =4004a(19) =4554a(20) =9504a(21) =10890a(22) =25740a(23) =29887a(24) =77077a(25) =90090a(26) =234454a(27) =273559a(28) =685984a(29) =795704