Number of nonempty subsets of {1,2,...,n} in which exactly 4/5 of the elements are <= (n+1)/3.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =0a(10) =7a(11) =8a(12) =9a(13) =45a(14) =50a(15) =55a(16) =165a(17) =180a(18) =195a(19) =455a(20) =490a(21) =525a(22) =1155a(23) =1240a(24) =1326a(25) =3366a(26) =3645a(27) =3933a(28) =11685a(29) =12750