Number of 4-cycles in the n X n rook graph.

Terms

a(0) =0a(1) =1a(2) =9a(3) =60a(4) =250a(5) =765a(6) =1911a(7) =4144a(8) =8100a(9) =14625a(10) =24805a(11) =39996a(12) =61854a(13) =92365a(14) =133875a(15) =189120a(16) =261256a(17) =353889a(18) =471105a(19) =617500a(20) =798210a(21) =1018941a(22) =1285999a(23) =1606320a(24) =1987500a(25) =2437825a(26) =2966301a(27) =3582684a(28) =4297510a(29) =5122125