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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =0a(10) =0a(11) =36a(12) =45a(13) =55a(14) =220a(15) =264a(16) =312a(17) =780a(18) =910a(19) =1050a(20) =3465a(21) =4220a(22) =5100a(23) =21420a(24) =26775a(25) =33117a(26) =118104a(27) =146300a(28) =179340a(29) =574644