Number of ways to arrange 6 nonattacking queens on the lower triangle of an n X n board.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =64a(9) =1644a(10) =19306a(11) =146718a(12) =820218a(13) =3670288a(14) =13846830a(15) =45661556a(16) =134896662a(17) =364019248a(18) =909633276a(19) =2129318414a(20) =4709083054a(21) =9912162234a(22) =19970298696a(23) =38707229282a(24) =72458290216a(25) =131476840106a(26) =231906957348