solve problem 7

Program.cs

@@ -58,6 +58,19 @@ namespace Euler {
   		return primes;
   	}
 
+  	static List<long> FirstNPrimes(long n) {
+  		var primes = new List<long>();
+  		primes.Add(2);
+  		for (int i = 3; ; i += 2) {
+  			if (IsPrime(i, primes)) {
+  				primes.Add(i);
+  				if (primes.Count == n) {
+  					return primes;
+  				}
+  			}
+  		}
+  	}
+
   	static long Problem3() {
   		long target = 600_851_475_143;
   		long targetSqrt = (long) Math.Sqrt(target);
@@ -120,8 +133,13 @@ namespace Euler {
     	return sum * sum - sumSq;
   	}
 
+  	static long Problem7() {
+  		List<long> primes = FirstNPrimes(10001);
+  		return primes[primes.Count - 1];
+  	}
+
     static void Main(string[] args) {
-      WriteLine(Problem6());
+      WriteLine(Problem7());
     }
   }
 }