Number of nonempty subsets of {1,2,...,n} in which exactly 1/3 of the elements are <= (n-4)/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =10a(6) =15a(7) =45a(8) =77a(9) =175a(10) =322a(11) =645a(12) =1245a(13) =2325a(14) =4651a(15) =8301a(16) =17061a(17) =29491a(18) =61915a(19) =104506a(20) =223210a(21) =369876a(22) =801291a(23) =1308427a(24) =2868531a(25) =4628151a(26) =10250141a(27) =16373521a(28) =36582385a(29) =57945537