function prettify_num($num){
    $text = array(
        0 => '',
        1 => '',
        2 => ' million',
        3 => ' billion',
        4 => ' trillion'
    );

    $exp = 3 * floor( ( strlen( (string) $num ) - 1 ) / 3);
    $rounded_num = round($num / pow(10, $exp), 1);
    if (($rounded_num / 100) > 1) $rounded_num = round($rounded_num);
    if (1 == ($exp / 3)) $rounded_num = number_format($rounded_num * 1000);
    return $rounded_num . $text[$exp / 3];
}