I do not understand your question. Your current script produces the following output:

1: 33
2: 45
3: 57
4: 69
5: 81
...
[download]

I modified your code so that it would print out the value of the $a variable in hexadecimal notation (with a "0x" prefix), using the Perl built-in function printf:

#!/usr/bin/env perl

use warnings;
use strict;
my $a=0x15;
for (my $i = 1; $i <= 100; $i++)
{
   $a+=0x0C;
   print "$i: ";
   printf "0x%x\n", $a;
}
[download]

This is the new output:

1: 0x21
2: 0x2d
3: 0x39
4: 0x45
5: 0x51
...
[download]

If this is not the output you are looking for, please provide a small sample of your desired output.

Please also state a reason why you do not want to use printf.