Number of nonempty subsets of {1,2,...,n} in which exactly 1/6 of the elements are <= (n-2)/3.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =1a(6) =6a(7) =12a(8) =42a(9) =112a(10) =168a(11) =378a(12) =759a(13) =1014a(14) =1914a(15) =3564a(16) =4620a(17) =9295a(18) =20020a(19) =27027a(20) =63083a(21) =146648a(22) =199304a(23) =456484a(24) =1007454a(25) =1339464a(26) =2896664a(27) =6165494a(28) =8093214a(29) =17441739