Number of transitive relations on an n-set with exactly five ordered pairs.

Terms

a(0) =0a(1) =0a(2) =0a(3) =27a(4) =768a(5) =8771a(6) =63468a(7) =340620a(8) =1470784a(9) =5371002a(10) =17153352a(11) =49075521a(12) =128066400a(13) =309124101a(14) =697874996a(15) =1486830618a(16) =3011414784a(17) =5833686340a(18) =10863883728a(19) =19532496375a(20) =34028554944a(21) =57623258007a(22) =95101946940a(23) =153331834040a(24) =241997811264a(25) =374544148830a(26) =569365964440a(27) =851301035325