euler27.c


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#include <stdio.h>
#include <stdlib.h>
#define MAX 3000000

int notPrime[MAX]={0};

void genprimes(int n)
{
	notPrime[0]=1;
	notPrime[1]=1;
	int i,j;
	for (i=2;i<=n;++i){
		if (!notPrime[i]){
			for (j=i*2;j<=n;j+=i){
				notPrime[j]=1;
			}
		}
	}
}
	
int main()
{
	int a,b,n;
	int product=0,longest=0;
	genprimes(MAX);
	for (a=-999;a<=999;a+=2){
		for (b=-997;b<=997;b+=2){
			if (notPrime[abs(b)])
				continue;
			for (n=0;;++n){
				int t=(n+a)*n+b;
				if (notPrime[abs(t)]){
					if (n>longest){
						longest = n;
						product = a*b;
					}
					break;
				}
			}
		}
	}
	printf("%d\n",product);
	return 0;
}