そすう

最速で素数を求めるほにゃららが酷かったので
以下

第一引数までの素数をコンソールに出力

prim.cs

namespace ConsoleApplication1
{
    class Program
    {
        private static int input;
        private static bool[] sieve;
        private static int limitSqrt;

        static void Main(string[] args)
        {
            input = int.Parse(args[0]);
            sieve = new bool[input + 1];
            limitSqrt = (int)System.Math.Sqrt((double)input);

            sieve[0] = false;
            sieve[1] = false;
            sieve[2] = true;
            sieve[3] = true;

            for (int x = 1 ; x <= limitSqrt ; x++)
            {
                for (int y = 1 ; y <= limitSqrt ; y++)
                {
                    int n = (4 * x * x) + (y * y);
                    if (n <= input && (n % 12 == 1 || n % 12 == 5))
                    {
                        sieve[n] = !sieve[n];
                    }
                    n = (3 * x * x) + (y * y);
                    if (n <= input && (n % 12 == 7))
                    {
                        sieve[n] = !sieve[n];
                    }
                    n = (3 * x * x) - (y * y);
                    if (x > y && n <= input && (n % 12 == 11))
                    {
                        sieve[n] = !sieve[n];
                    }
                }
            }
            for (int m = 5; m <= limitSqrt; m++)
            {
                if (sieve[m])
                {
                    int m2 = m * m;
                    for (int i = m2; i <= input ; i += m2)
                    {
                        sieve[i] = false;
                    }
                }
            }
            for (int i = 0 ; i <= input ; i++)
            {
                if (sieve[i])
                {
                    System.Console.Write(i.ToString() + ",");
                }
            }
        }
    }
}