Number of ways to arrange 4 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) =8a(6) =118a(7) =802a(8) =3708a(9) =13280a(10) =39734a(11) =104000a(12) =244948a(13) =530632a(14) =1072776a(15) =2048056a(16) =3723314a(17) =6492342a(18) =10915254a(19) =17777372a(20) =28147380a(21) =43465356a(22) =65624634a(23) =97098802a(24) =141050688a(25) =201509798a(26) =283514112a(27) =393348562a(28) =538725268a(29) =729098516