$num = 1234567;
$base = 16;
$result = "";
my @digit = (0 .. 9, 'A' .. 'Z');
do {
    use integer;
    my $digit = $num % $base;
    substr($result, 0, 0) = $digit[$digit]; # for base up to 36
    $num /= $base;
} while $num;
print $result;