Turn a number into an Excel column name

#!/home/ben/software/install/bin/perl
use warnings;
use strict;

# Just for testing. Save the output as test.csv and open in Excel.

for my $i (1..256) {
    print ntol($i), ", ";
}

# Convert a number from 1 to 26 into a letter from A to Z.

sub _number_to_letter
{
    my ($number) = @_;
    if ($number > 26) {
        die "Number $number out of range";
    }
    my $letter = chr ($number+ord("A"));
    return $letter;
}

# Convert a number into an Excel column name.

sub ntol
{
    # The maximum number of columns in an Excel worksheet is ...
    my $max_excel_column = 256;

    my ($n) = @_;
    my $l;
    if ($n >= 1 && $n <= 26) {
        $l = _number_to_letter ($n - 1);
    } elsif ($n > 26 && $n <= $max_excel_column) {
        my $chr1 = _number_to_letter (int (($n - 1)/26 - 1));
        my $chr2 = _number_to_letter (($n - 1) % 26);
        $l = $chr1 . $chr2;
    } else {
        die "number $n out of Excel's column range (1-$max_excel_column)";
    }
    return $l;
}