写了个求梅森素数的程序，输出不正确，求指教,该怎么处理

写了个求梅森素数的程序，输出不正确，求指教

C/C++ code


#include<stdio.h>

int expo = 2;
int divisor = 2;
int square = 0;
unsigned long long MersennePrime = 3;//Mersenne prime number(2^p-1)
unsigned long long MersennePrimePlus1 = 4;//Mersenne prime number plus 1 (2^p)

int isPrime(unsigned long long number)
{
    if(number ==2)
    {
        return 1;
    }
    divisor = 2;
    square = (divisor) * (divisor);
    while(square<=number)
    {
        if(number%divisor==0)
        {
            return 0;//Not prime, return false
        }
        divisor++;
        square = (divisor) * (divisor);
    }
    return 1;//else return true
}

void Mersenne(int a)
{
    if(a>=0&&a<=10)
    {
        unsigned long long MersennePrime = 3;
        unsigned long long MersennePrimePlus1 = 4;
        printf("%d mers = ",a);
        expo = 2;
        while(a>0)
        {
            if(isPrime(MersennePrime)&&isPrime(expo))
            {
                printf("%llu ",MersennePrime);
                a--;
            }
            MersennePrimePlus1 = MersennePrimePlus1 * 2;
            MersennePrime = MersennePrimePlus1 - 1;
            expo++;
        }
        printf("\n");
    }else
    {
        printf("This program can only compute up to 10 Mersenne primes\n");
    }
}


int main(){
    Mersenne(10);
    getchar();
    return 0;
}

1到8还有第10个都是梅森素数，但是第9个不是，算了下是2^59-1，59也是素数，是我isPrime写错了么？该如何改正？谢谢
（我的思路是用求平方根限定约数的范围，但是作业要求只能用stdio.h不能用math等library，所以我就自己写了个了，思路是如果divisor的平方大于number就跳出循环，问题是所有数字都是正确的只有第9个不对，我用isPrime方法求前1000个质数，跟我用一般的方法求的答案也是对的，找了很久都找不到第9个数错的原因，只好上来求救了）

------解决方案--------------------
#include<stdio.h>

unsigned long long expo = 2;
unsigned long long divisor = 2;
int square = 0;
unsigned long long MersennePrime = 3;//Mersenne prime number(2^p-1)
unsigned long long MersennePrimePlus1 = 4;//Mersenne prime number plus 1 (2^p)

int isPrime(unsigned long long number)
{
if(number ==2)
{
return 1;
}
divisor = 2;
square = (divisor) * (divisor);
while(square<=number)
{
if(number%divisor==0)
{
return 0;//Not prime, return false
}
divisor++;
square = (divisor) * (divisor);
}
return 1;//else return true
}

void Mersenne(int a)
{
if(a>=0&&a<=10)
{
unsigned long long MersennePrime = 3;
unsigned long long MersennePrimePlus1 = 4;
printf("%d mers = ",a);
expo = 2;
while(a>0)
{
if(isPrime(MersennePrime)&&isPrime(expo))
{
printf("%llu ",MersennePrime);
a--;
}
MersennePrimePlus1 = MersennePrimePlus1 * 2;
MersennePrime = MersennePrimePlus1 - 1;
expo++;
}
printf("\n");
}else
{
printf("This program can only compute up to 10 Mersenne primes\n");
}
}

int main(){
Mersenne(10);
getchar();
return 0;
}

写了个求梅森素数的程序，输出不正确，求指教,该怎么处理

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