Number of nonempty subsets of {1,2,...,n} in which exactly 4/5 of the elements are <= (n-1)/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =5a(9) =6a(10) =30a(11) =35a(12) =105a(13) =120a(14) =280a(15) =315a(16) =666a(17) =745a(18) =1665a(19) =1881a(20) =4785a(21) =5490a(22) =14850a(23) =17160a(24) =45331a(25) =52339a(26) =131859a(27) =151775a(28) =371735a(29) =427336