php program for fibonacci series

<?php

//variable initialization
$count = 0 ;
$f1 = 0;
$f2 = 1;

echo $f1." , ";
echo $f2." , ";

  while ($count < 20 ) { 

    $f3 = $f2 + $f1 ;
    echo $f3." , ";
    $f1 = $f2 ;
    $f2 = $f3 ;
    $count = $count + 1;

  } 

?>