Number of nonempty subsets of {1,2,...,n} in which exactly 1/2 of the elements are <= (n+2)/3.

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =9a(5) =14a(6) =34a(7) =55a(8) =83a(9) =209a(10) =329a(11) =494a(12) =1286a(13) =2001a(14) =3002a(15) =8007a(16) =12375a(17) =18563a(18) =50387a(19) =77519a(20) =116279a(21) =319769a(22) =490313a(23) =735470a(24) =2042974a(25) =3124549a(26) =4686824a(27) =13123109a(28) =20030009a(29) =30045014