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

Terms

a(0) =0a(1) =0a(2) =0a(3) =3a(4) =4a(5) =14a(6) =20a(7) =55a(8) =83a(9) =209a(10) =329a(11) =791a(12) =1286a(13) =3002a(14) =5004a(15) =11439a(16) =19447a(17) =43757a(18) =75581a(19) =167959a(20) =293929a(21) =646645a(22) =1144065a(23) =2496143a(24) =4457399a(25) =9657699a(26) =17383859a(27) =37442159a(28) =67863914a(29) =145422674