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

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =6a(5) =13a(6) =21a(7) =45a(8) =70a(9) =154a(10) =235a(11) =525a(12) =791a(13) =1793a(14) =2681a(15) =6153a(16) =9150a(17) =21206a(18) =31401a(19) =73359a(20) =108262a(21) =254607a(22) =374715a(23) =886171a(24) =1301235a(25) =3091971a(26) =4531423a(27) =10811671a(28) =15818791a(29) =37877401