<?php
$num = 0; $n1 = 0; $n2 = 1;
echo "$n1 $n2 ";
while ($num < 20 ) {
    $n3 = $n2 + $n1;
    echo "$n3 ";
    $n1 = $n2;
    $n2 = $n3;
    $num = $num + 1;
}