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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =10a(7) =20a(8) =35a(9) =105a(10) =168a(11) =252a(12) =588a(13) =930a(14) =1452a(15) =3960a(16) =6820a(17) =11440a(18) =30745a(19) =52507a(20) =86905a(21) =219765a(22) =372120a(23) =617610a(24) =1572228a(25) =2702252a(26) =4563344a(27) =11666760a(28) =20167170a(29) =34220634