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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =6a(10) =7a(11) =35a(12) =40a(13) =120a(14) =135a(15) =315a(16) =350a(17) =745a(18) =825a(19) =1881a(20) =2106a(21) =5490a(22) =6240a(23) =17160a(24) =19635a(25) =52339a(26) =59855a(27) =151775a(28) =173160a(29) =427336