Number of nonempty subsets of {1,2,...,n} in which exactly 1/4 of the elements are <= (n-3)/3.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =10a(6) =20a(7) =35a(8) =77a(9) =140a(10) =252a(11) =505a(12) =1000a(13) =1936a(14) =3652a(15) =7305a(16) =14313a(17) =25805a(18) =52325a(19) =104651a(20) =184736a(21) =379676a(22) =769556a(23) =1334942a(24) =2764139a(25) =5654894a(26) =9685364a(27) =20191604a(28) =41641244a(29) =70639794