#!/usr/bin/perl -w
use strict;

foreach (1..15)
{
   print fibonacci($_), " ";
}
# prints: 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 

sub fibonacci
{
     my $number = shift;

     my $cur_num   = 1;
     my $prev_num  = 1;
     my $sum;
     
     return 1  if ($number == 1 || $number == 2);
   
   # to get Op's output, supress the above by this:  
   # return "" if ($number == 1 || $number == 2);
   # or of course just start the sequence at a different number
     
     $number -= 2;
   
     while ($number--)
     {
         $sum = $cur_num + $prev_num;
         $prev_num = $cur_num;
         $cur_num  = $sum;
     }
   
     return $sum;
}