function prettify_num($num){
    $text = array(
        1 => 'thousand',
        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);


    return $rounded_num .' '. $text[$exp / 3];
}