C# solution with comments:

public static string counterGame(long n)

    {

            bool currentPlayer1 = true;


    while(n > 1)
    {   
        // Check if n is a power of 2
        //A number is a power of 2 if it has exactly one 1 bit in its binary representation. (i.e. 100)         
        if((n & (n - 1)) == 0)
        {
            n = n/2;             
        }
        else
        {             
            //Math.Log(n, 2) -  Math.Log(20, 2) will return approximately 4.32 because 2 4.32 = 20
            //Math.Floor(4.32) round down, so will produce 4.
            //Math.Pow(2, 4) which will produce 16
            //So finally 20 - 16, will give 4, which will be the new number for the next turn.
            long largestPowerOf2 = (long)Math.Pow(2, (long)Math.Floor(Math.Log(n, 2)));
            n -= largestPowerOf2;                                
        }

        currentPlayer1 = !currentPlayer1;

    }

    return currentPlayer1 ? "Richard" : "Louise";
}