A143891 Number of ways of placing kings with no more than 4 mutual attacks on an n X n chessboard symmetric about the diagonal and under 90-degree rotation.
1, 2, 1, 5, 2, 15, 7, 68, 23, 370, 104, 2649, 571, 25209, 4176, 313503, 39827, 5212881, 500254, 114569731, 8348616
Offset: 0