How to fill in a matrix recursively in c++?

So I have to fill in a square matrix recursively. For size N=5, it should be:

  1 1 1 1 1
  1 2 2 2 1
  1 2 3 2 1
  1 2 2 2 1
  1 1 1 1 1

but my program shows:

  1 1 1 1 1
  1 2 2 2 1
  1 2 3 3 1
  1 2 2 2 1 
  1 1 1 1 1 

void llenar5 (int** mat, int n, int f=0, int c=0,int k=2)
{
if (f<n)
{
    if (c<n)
    {
        if (f==0 ||c==0||f==n-1||c==n-1)
        {
            *(*(mat+f)+c)=1; 
            llenar5(mat,n,f,c+1,k); //move to the right
        }
        else if (f==k-1 ||c==k-1||f==n-k||c==n-k)
        {
            *(*(mat+f)+c)=k;
            llenar5(mat,n,f,c+1,k++);
        }
    }
    llenar5(mat,n,f+1,c,k);
}

}

I am creating a matrix in dynamic memory, and I tried calling the function llenar5(mat,n,f+1,c+1,k+1) to jump a column and row while incrementing the values.