Number of ways to arrange 3 nonattacking queens on the lower triangle of an n X n board.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =12a(5) =82a(6) =330a(7) =1008a(8) =2566a(9) =5742a(10) =11652a(11) =21926a(12) =38802a(13) =65322a(14) =105428a(15) =164214a(16) =248022a(17) =364764a(18) =523998a(19) =737334a(20) =1018488a(21) =1383768a(22) =1852104a(23) =2445628a(24) =3189660a(25) =4113396a(26) =5249848a(27) =6636636a(28) =8315880a(29) =10335110