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

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =6a(5) =13a(6) =25a(7) =45a(8) =91a(9) =175a(10) =322a(11) =570a(12) =975a(13) =1617a(14) =2607a(15) =7425a(16) =12753a(17) =21385a(18) =35065a(19) =56302a(20) =88638a(21) =136986a(22) =208050a(23) =310840a(24) =1251606a(25) =1973706a(26) =3065931a(27) =4694921a(28) =7092211a(29) =10575635