Number of nonempty subsets of {1,2,...,n} in which exactly 3/5 of the elements are <= (n-1)/3.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =21a(10) =28a(11) =36a(12) =144a(13) =180a(14) =220a(15) =550a(16) =660a(17) =780a(18) =2275a(19) =2821a(20) =3465a(21) =13230a(22) =16940a(23) =21420a(24) =74256a(25) =94248a(26) =118104a(27) =367080a(28) =461700a(29) =574644