telephone number
... that the number of ways to place n diagonally symmetric rooks on an n × n chessboard in such a way that no two rooks attack each other is a telephone number?
... that the number of ways to place <i id="mwAp0">n</i> diagonally symmetric <a href="./Rook_(chess)" id="mwAp4" rel="mw:WikiLink" title="Rook (chess)">rooks</a> on an <i id="mwAp8">n</i><span id="mwAqA" typeof="mw:Entity"> </span><span id="mwAqE" typeof="mw:Entity">×</span><span id="mwAqI" typeof="mw:Entity"> </span><i id="mwAqM">n</i> <a href="./Chessboard" id="mwAqQ" rel="mw:WikiLink" title="Chessboard">chessboard</a> in such a way that no two rooks attack each other is a <b id="mwAqU"><a href="./Telephone_number_(mathematics)" id="mwAqY" rel="mw:WikiLink" title="Telephone number (mathematics)">telephone number</a></b>?