How to invert an integer?

One solution would be to use this function that I created:

 public static void Inverter(int numero)
        {

            string valor = numero.ToString();
            string resultado = "";
            for(int i = valor.Length; i >0; i--)
            {
                resultado += valor[i-1];
            }


            Console.WriteLine(valor);
        }

In this case the value 123 for example would try to execute 123 times in its for, while we have only 3 characters, which caused in its error: ArgumentOutOfRangeException

   string s = Convert.ToString(n);
   for (int i = n; i > 0; i--)

Change needed in your code:

Console.Write("Informe um número inteiro para ser invertido: ");
        int n = Convert.ToInt32(Console.ReadLine());
        string s = Convert.ToString(n);
        string resultado = "";

        for (int i = n.ToString().Length; i > 0; i--)
        {
            string a = s.Substring(i - 1, 1);
            resultado += a;
        }
        Console.WriteLine(resultado);

Points I've changed:

Usually these exercises are to demonstrate the ability to assemble the best algorithm, and not go the easy way, so I would do mathematically.

I have taken care of fixing the problem so that if the typing is not valid, it will break the application. I also did the validation that the statement requested.

using static System.Console;

public class Program {
    public static void Main() {
        Write("Informe um número inteiro para ser invertido: ");
        if (!int.TryParse(ReadLine(), out var numero) && numero >= 0) return;
        var invertido = 0;
        while (numero > 0) {
           invertido = invertido * 10 + numero % 10;
           numero /= 10;
        }
        WriteLine(invertido);
    }
}

See running on .NET Fiddle . And no Coding Ground . Also I placed GitHub for future reference .

If you really want to do with string do it the right way, for an exercise you do not need:

using static System.Console;
using System.Text;

public class Program {
    public static void Main() {
        Write("Informe um número inteiro para ser invertido: ");
        var texto = ReadLine();
        if (!int.TryParse(texto, out var numero) && numero >= 0) return;
        var invertido = new StringBuilder(texto.Length);
        for(int i = texto.Length - 1; i >= 0; i--) invertido.Append(texto[i]);
        WriteLine(invertido);
    }
}

See running on .NET Fiddle . Also I put GitHub for future reference .

Analyzing the code

There are some errors in your implementation. I made the corrections and I will comment below.

Console.Write("Informe um número inteiro para ser invertido: ");
string numeroDigitado = Console.ReadLine();
int numeroConvertido = Int32.Parse(numeroDigitado);
string invertido = "";

for (int i = numeroDigitado.Length; i > 0; i--) {
    string letra = numeroDigitado.Substring(i - 1, 1);
    invertido += letra;
}

Console.WriteLine(invertido);

First I changed the name of your variables to make it a little easier to read. This is not a rule.

Before you were getting a string from the Console, converting it to integer and then converting to string again, one of those conversions is unnecessary. You can see my changes on lines 2 and 3.

Your for was starting at n , which was your integer converted. The correct would be to vary by the number of characters of the number. 1235 must iterate 4 times, not 1235 times.

Another solution

An easy manipulation would be to take this integer and convert it to a vector of characters using the .ToCharArray() method, invert this array and return to integer.

public int ReverseInt(int input) {
    char[] vetor = input.ToString().ToCharArray();
    Array.Reverse(vetor);
    return Int32.Parse(new String(vetor));
}