Factor Table

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        public static int FirstFactor(int num)
        {
            if (num % 2 == 0)
                return 2;
            for (int i = 3; i <= num / 2; i++)
                if (num % i == 0)
                {
                    bool isPrime = true;
                    for (int j = 2; j < i; j++)
                        if (i % j == 0)
                            isPrime = false;
                    if (isPrime)
                        return i;
                }
            return 0;
        }
        static void Main(string[] args)
        {
            string[] output = new string[100];
            output[0] = "";
                for (int j = 0; j <= 10; j++)
                {
                    output[0] += "    ";
                }
                for (int i = 1; i < output.Length; i++)
                    output[i] = output[0];
                Console.Write(' ');
            for (int j = 0; j <= 9; j++)
                Console.Write("   " + j);
            Console.WriteLine();
            for (int i = 0; i <= 99; i++)
            {
                output[i] = output[i].Remove(0, i.ToString().Length);
                output[i] = output[i].Insert(0, i.ToString());
                for (int j = 0; j <= 9; j++)
                {
                    int firstFactor = FirstFactor(j * 100 + i);
                    if (firstFactor != 0)
                    {
                        output[i] = output[i].Remove((j + 1) * 4, firstFactor.ToString().Length);
                        output[i] = output[i].Insert((j + 1) * 4, firstFactor.ToString());
                    }
                }
            }
            output[0] = output[0].Remove(4, 4);
            output[0] = output[0].Insert(4, "    ");
            output[1] = output[1].Remove(4, 4);
            output[1] = output[1].Insert(4, "    ");
            for (int i = 0; i < output.Length; i++)
                Console.WriteLine(output[i]);
        }
    }
}