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

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =6a(5) =9a(6) =21a(7) =30a(8) =70a(9) =100a(10) =235a(11) =335a(12) =791a(13) =1127a(14) =2681a(15) =3822a(16) =9150a(17) =13050a(18) =31401a(19) =44802a(20) =108262a(21) =154517a(22) =374715a(23) =534963a(24) =1301235a(25) =1858155a(26) =4531423a(27) =6472167a(28) =15818791a(29) =22597759