Integer to Alphabet string ("A", "B", ...."Z", "AA", "AB"...)
Math! Simple math is certainly the nicest way, no lists to deal with, just old fashion ASCII and math. If you want to be able to toggle the capitalization of this method, simply use a ternary operator like this isCapital ? 'A' : 'a' I just left it capital as that is how the OP seemed to want it. Jeff Mercado's Answer explained well enough the differences between calculated, recursive and such... I mostly wanted to provide a simplistic calculated answer that did not involve using lists.

public static string IntToLetters(int value)
{
    string result = string.Empty;
    while (--value &gt;= 0)
    {
        result = (char)('A' + value % 26 ) + result;
        value /= 26;
    }
    return result;
}


Edit: To meet the requirement of A being 1 instead of 0, I've added -- to the while loop condition, and removed the value-- from the end of the loop, if anyone wants this to be 0 for their own purposes, you can reverse the changes, or simply add value++; at the beginning of the entire method.