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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =4a(9) =5a(10) =30a(11) =36a(12) =126a(13) =147a(14) =392a(15) =448a(16) =1008a(17) =1134a(18) =2304a(19) =2565a(20) =5115a(21) =5687a(22) =12342a(23) =13860a(24) =34320a(25) =39039a(26) =104104a(27) =119119a(28) =315679a(29) =360815