Number of nonempty subsets of {1,2,...,n} in which exactly 2/5 of the elements are <= (n-3)/3.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =35a(9) =56a(10) =84a(11) =252a(12) =360a(13) =495a(14) =1452a(15) =2244a(16) =3432a(17) =11440a(18) =18655a(19) =29575a(20) =86905a(21) =139960a(22) =220150a(23) =617610a(24) =1007216a(25) =1616615a(26) =4563344a(27) =7573970a(28) =12359690a(29) =34220634