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#include <stdio.h>
#include <math.h>
long isprime(long n);
long n2n41(long n);
int primepct[10001];
int main(int argc, char **argv)
{
long a, b, i, ip;
int notprime, prime;
for(i = 0; i < 10001; i++)
{
primepct[i] = 0;
}
while (scanf("%ld %ld", &a, &b) != EOF)
{
for(i = a; i <= b; i++)
{
if(primepct[i-1]==0)
{
if(isprime(n2n41(i))==0)
{
prime++;
primepct[i-1] = 1;
}
else
{
notprime++;
primepct[i-1] = -1;
}
}
else
{
if(primepct[i-1]==1)
{
prime++;
}
else
{
notprime++;
}
}
}
printf("%.2f\n", floor(((double)prime/(prime+notprime))*10000+.5)/100);
notprime = 0;
prime=0;
}
return 0;
}
long n2n41(long n)
{
return n*n+n+41;
}
long isprime(long n)
{
long i = 3;
long sqn = 0;
while (n%2==0)
{
n /= 2;
return 1;
}
sqn = (sqrt(n))+1;
while (i <= sqn)
{
if ((n%i)==0)
{
n /= i;
return 1;
}
else
{
i += 2;
}
}
return 0;
}
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