Hexadecimal format specifier not working

for(int X = 1 ; X <= 5 ; X++)
{
    var F = Math.Pow(63, X);
    Console.WriteLine($"{F:X}");
}

For some reason this is not working and I receive an error: FormatException: Format specifier was invalid.

And even if I try F.ToString("X") it's also not working

It's because your variable F is a floating point number. It needs to be an integer.

Also don't use capital letters for variable names.

Okay, that worked! I didn't know it works only for integers, thanks!