Problem 27
using System;
class PE027 {
static bool IsPrime(int n) {
if (n <= 1) return false;
if (n == 2) return true;
if (n % 2 == 0) return false;
for (int i = 3; i*i <= n; i += 2) {
if (n % i == 0)
return false;
}
return true;
}
static void Main() {
int maxlen = 0;
int ans = 0;
for (int b = 2; b < 1000; b++) {
if (!IsPrime(b)) continue;
for (int a = -999; a < 1000; a++) {
for (int i = 0; ; i++) {
int x = i*i + a*i + b;
if (!IsPrime(x)) {
if (maxlen < i-1) {
maxlen = i-1;
ans = a * b;
}
break;
}
}
}
}
Console.WriteLine(ans);
}
}