How to Generate Random Numbers in c#

using System.Security.Cryptography;

using System.Text;

string randomnumber=GetRandomKey(4);

private string GetRandomKey(int len)
{
int maxSize = len;
char[] chars = new char[30];
string a;
a = "1234567890";
chars = a.ToCharArray();
int size = maxSize;
byte[] data = new byte[1];
RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider();
crypto.GetNonZeroBytes(data);
size = maxSize;
data = new byte[size];
crypto.GetNonZeroBytes(data);
StringBuilder result = new StringBuilder(size);
 foreach (byte b in data) { result.Append(chars[b % (chars.Length)]); }
return result.ToString();
}

o/p:

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