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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =3a(8) =4a(9) =24a(10) =30a(11) =105a(12) =126a(13) =336a(14) =392a(15) =882a(16) =1008a(17) =2044a(18) =2304a(19) =4554a(20) =5115a(21) =10890a(22) =12342a(23) =29887a(24) =34320a(25) =90090a(26) =104104a(27) =273559a(28) =315679a(29) =795704