There are several pieces of chess pieces that can be arranged into a square matrix of 9 pieces on each side. What is the total number of pieces?
棋子若干枚，恰好可以排成每边9枚的方阵，棋子总数是多少？
<gadget id="calculator">9 * 9</gadget>
<output>81</output>

<result>81</result>