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

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =3a(5) =9a(6) =14a(7) =34a(8) =55a(9) =125a(10) =209a(11) =461a(12) =791a(13) =1715a(14) =3002a(15) =6434a(16) =11439a(17) =24309a(18) =43757a(19) =92377a(20) =167959a(21) =352715a(22) =646645a(23) =1352077a(24) =2496143a(25) =5200299a(26) =9657699a(27) =20058299a(28) =37442159a(29) =77558759