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

Terms

a(0) =0a(1) =0a(2) =5a(3) =27a(4) =90a(5) =230a(6) =495a(7) =945a(8) =1652a(9) =2700a(10) =4185a(11) =6215a(12) =8910a(13) =12402a(14) =16835a(15) =22365a(16) =29160a(17) =37400a(18) =47277a(19) =58995a(20) =72770a(21) =88830a(22) =107415a(23) =128777a(24) =153180a(25) =180900a(26) =212225a(27) =247455a(28) =286902a(29) =330890