1. 鏌愮數褰遍櫌鍏辨湁20鎺掑骇浣嶏紟宸茬煡绗涓鎺掓湁18搴э紝鍚庨潰姣忔帓閮芥瘮鍓嶄竴鎺掑2涓搴т綅锛庯紙1锛夊啓鍑鸿$畻绗琻鎺掔殑搴т綅鏁癮 n
锛1锛変緷棰樻剰寰楋細澧炲姞鐨勫骇浣嶆暟涓猴細2锛坣-1锛=2n-2鈭碼n=2n-2+18=2n+16锛2锛夊綋n=20鏃讹紝a20=56锛