This uses Fermat's theorem and Euler's formula. This formula can be written as follows: (3d- 1)=20*n, where n is an integer, which means that the value of 3d- 1 is a multiple of 20, which is not comprehensive. When d=7, n= 1, which holds; When n=2 and d=27, this formula still holds. According to RSA principle, the following C language can be used to find the value of d. ...