Number of ways to place 3 nonattacking semi-queens on an n X n board.

Terms

a(0) =0a(1) =0a(2) =3a(3) =52a(4) =370a(5) =1620a(6) =5285a(7) =14168a(8) =33012a(9) =69240a(10) =133815a(11) =242220a(12) =415558a(13) =681772a(14) =1076985a(15) =1646960a(16) =2448680a(17) =3552048a(18) =5041707a(19) =7018980a(20) =9603930a(21) =12937540a(22) =17184013a(23) =22533192a(24) =29203100a(25) =37442600a(26) =47534175a(27) =59796828a(28) =74589102a(29) =92312220