Number of ways to place 4 nonattacking amazons (superqueens) on an n X n board.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =2a(5) =112a(6) =1754a(7) =13074a(8) =63400a(9) =234014a(10) =712248a(11) =1882132a(12) =4457246a(13) =9679760a(14) =19584514a(15) =37367934a(16) =67849336a(17) =118085614a(18) =198107620a(19) =321870956a(20) =508359070a(21) =782972820a(22) =1179105738a(23) =1740089734a(24) =2521359260a(25) =3593085246a(26) =5043058972