C program to find the largest prime number below 5000, test a prime number

/*to find the largest  prime number below 5000*/

#include<stdio.h>

#include<math.h>

void

main()

{

                int n,i,remainder,d,c=0;

                for(n=5000;n>=3;n--)

                {

                                d=sqrt(n);

   for(i=2;i<d;i++)

   {

                   remainder=n%i;

                   if(remainder==0)

                                   goto label;

                   }

                   if(n>c)

                                   c=n;

   }

label:;

                }

                printf("the largest prime number %d is\n",c);

}

Result:

the largest prime number 4999 is

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/*test a prime number (2^(2^n))+1  */

#include<stdio.h>

#include<math.h>

void

main()

{

                int n,i,remainder,d,m1,m;

                for(n=1;n<=4;n++)

                {

                                m1=(pow(2,n));

                                m=(pow(2,m1)+1);

                                d=sqrt(m);

                                for(i=2;i<d;i++)

                                {

                                                remainder=m%i;

                                                if(remainder==0)

                                                {

                                                                goto label;

                                }

                                }

                                printf("the number %d is prime\n",m);

label:;

                }

}

Result:

the number 5 is prime

the number 17 is prime

the number 257 is prime

the number 65537 is prime

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