Number of ways of placing n nonattacking queens on an n X n board.

Terms

a(0) =1a(1) =1a(2) =0a(3) =0a(4) =2a(5) =10a(6) =4a(7) =40a(8) =92a(9) =352a(10) =724a(11) =2680a(12) =14200a(13) =73712a(14) =365596a(15) =2279184a(16) =14772512a(17) =95815104a(18) =666090624a(19) =4968057848a(20) =39029188884a(21) =314666222712