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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =6a(8) =7a(9) =8a(10) =24a(11) =27a(12) =30a(13) =105a(14) =121a(15) =138a(16) =450a(17) =520a(18) =595a(19) =1939a(20) =2255a(21) =2600a(22) =8456a(23) =9877a(24) =11445a(25) =37122a(26) =43510a(27) =50625a(28) =164025a(29) =192801