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

Terms

a(0) =0a(1) =0a(2) =0a(3) =2a(4) =3a(5) =4a(6) =5a(7) =6a(8) =18a(9) =21a(10) =24a(11) =27a(12) =30a(13) =33a(14) =36a(15) =138a(16) =156a(17) =175a(18) =195a(19) =216a(20) =238a(21) =261a(22) =285a(23) =310a(24) =1150a(25) =1260a(26) =1375a(27) =1495a(28) =1620a(29) =1750