Fastest function to generate Excel column letters in C#

Question

What is the fastest c# function that takes and int and returns a string containing a letter or letters for use in an Excel function? For example, 1 returns \"A\", 26 return

Answer 1

@Neil N -- nice code I think the thirdLetter should have a +64 rather than +65 ? am I right?

public string Letter(int intCol) {

    int intFirstLetter = ((intCol) / 676) + 64;
    int intSecondLetter = ((intCol % 676) / 26) + 64;
    int intThirdLetter = (intCol % 26) + 65;  ' SHOULD BE + 64?

    char FirstLetter = (intFirstLetter > 64) ? (char)intFirstLetter : ' ';
    char SecondLetter = (intSecondLetter > 64) ? (char)intSecondLetter : ' ';
    char ThirdLetter = (char)intThirdLetter;

    return string.Concat(FirstLetter, SecondLetter, ThirdLetter).Trim();
}