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

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =8a(6) =20a(7) =30a(8) =63a(9) =86a(10) =182a(11) =245a(12) =560a(13) =756a(14) =1784a(15) =2387a(16) =5600a(17) =7400a(18) =17336a(19) =22737a(20) =53850a(21) =70390a(22) =168610a(23) =219791a(24) =529529a(25) =688051a(26) =1662907a(27) =2154347a(28) =5225636a(29) =6754580