c# 数字问题

如果都是一位数的话
using System;

namespace ConsoleApplication4
{
class Program
{
static void Main(string[] args)
{
int n = 11;
int[,] nn = new int[n, n];
for (int k = 0; k < n; k++)
{
for (int i = k; i < n-k; i++)
{
for (int j = k; j < n-k; j++)
{
nn[i, j] = k+1;
}
}
}
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
Console.Write(nn[i, j]);
}
Console.WriteLine();
}
}
}
}