有乘法算式如下：

○○○

× ○○

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○○○○

○○○○

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○○○○○

18个○的位置上全部是素数(1、3、5或7)，请还原此算式。

*问题分析与算法设计

问题中虽然有18数位，但只要确定乘数和被乘数后经过计算



就可确定其它的数位。-multiplication formula is as follows : 2000 2000 --- --- 2000 2000 --- --- 2000 18 hours position all prime numbers (1, 3, 5 or 7), this reduction formula. * Analysis and design of algorithms Although the number of 18-bit, but as long as the multiplicand and multiplier determined after a calculation can be determined by several other.