Number of ways to place 4 nonattacking zebras on an n X n board.

Terms

a(0) =0a(1) =1a(2) =126a(3) =1168a(4) =7334a(5) =35749a(6) =137970a(7) =438984a(8) =1208246a(9) =2969389a(10) =6662480a(11) =13873100a(12) =27144408a(13) =50389581a(14) =89424014a(15) =152638280a(16) =251834530a(17) =403250693a(18) =628798516a(19) =957543164a(20) =1427453780a(21) =2087456085a(22) =2999819778a(23) =4242915176