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

Terms

a(0) =0a(1) =0a(2) =0a(3) =3a(4) =6a(5) =13a(6) =25a(7) =45a(8) =91a(9) =154a(10) =322a(11) =525a(12) =1125a(13) =1793a(14) =3921a(15) =6153a(16) =13671a(17) =21206a(18) =47718a(19) =73359a(20) =166800a(21) =254607a(22) =583947a(23) =886171a(24) =2047375a(25) =3091971a(26) =7188451a(27) =10811671a(28) =25272481a(29) =37877401