Fibonacci sequence generator

<?php

$results = [];
$results[0] = gmp_init(1);
$results[1] = gmp_init(1);

$n = $argv[1] ?? 1000;

if ($n < 2 || $n > PHP_INT_MAX) {
    throw new InvalidArgumentException('N cannot be less than 2 or greater than ' . number_format(PHP_INT_MAX) . '.');
}

echo 'Generating ' . number_format($n) . ' Fibonacci numbers ... ';

$start = microtime(true);

foreach (range(2, $n - 1) as $i) {
    $fib = gmp_add($results[$i - 2], $results[$i - 1]);

    $results[$i] = $fib;
}

echo 'done in ' . (string) round(microtime(true) - $start, 5) . ' seconds.' . "\n";

readline('Press any key to dump results ... ');

var_dump($results);

Results:
Generating 1,000 Fibonacci numbers ... done in 0.00045 seconds.

This is the 1000th Fibonacci number

434665576869374564356885276750406258025646605173717804024817290895365554179490518904038798
40079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795
166849228875