# 1015. Reversible Primes

Source: Internet
Author: User

A reversible prime in any number system was a prime whose "reverse" in the that number system is also a prime. For example in the decimal system are a reversible prime because its reverse PNS is also a prime.

Now given any of positive integers n (<5) and D (1 < D <=), you be supposed to tell if N is a Reversi Ble prime with radix D.

Input Specification:

The input file consists of several test cases. Each case occupies a line which contains the integers N and D. The input is finished by a negative N.

Output Specification:

For the test case, the print in one line "Yes" if N is a reversible prime with radix D, or "No" if not.

The problem is that the number of prime N is reversed in radix, and it is also prime in decimal.

23 is prime, binary means 10111, inversion 11101, decimal number is 29, I'm tangled.

`#include <stdio.h> #include <stdlib.h> #include <string.h> #include <math.h>bool isprime (int     num) {if (num==2) return true;     if (num<2) return false;     int temp= (int) sqrt (num*1.0);     for (int i=2;i<=temp;i++) if (num%i==0) return false;     return true;    }int Main () {int d,n;          while (scanf ("%d", &n) &&n>=0) {int revers[100000],i=0,num=0;          scanf ("%d", &d);                   if (IsPrime (n)) {while (n) {revers[i++]=n%d;                   n=n/d;                   printf ("%d", revers[i-1]);                   } for (int j=0;j<i-1;j++) {num= (revers[j]+num) *d;              } Num+=revers[i-1];              printf ("\n%d", num);              if (IsPrime (num)) printf ("yes\n");              else printf ("no\n");          } else printf ("no\n");    } system ("Pause");    return 0; }`

1015. Reversible Primes

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