Matrix of numbers

using System;
class MatrixOfNumbers
{
    static void Main()
    {
        Console.Write("Enter a positive integer number (0 < n < 21) : ");
        int n = int.Parse(Console.ReadLine());
        if (1<=n&&n<=20)
        {
            for (int i = 1; i <= n; i++)
            {
                Console.Write(i+" ");
                for (int j = i+1; j <=(n-1)+i; j++)
                Console.Write("{0} ",j);
                Console.WriteLine();
            }
        }
        else
        {
            Console.WriteLine("Invalid input!");
        }
    }
}