generates a pin code with numbers next to each other

pin.php

<?php

$num = [
	1 => [2, 4],
	2 => [1, 3, 5],
	3 => [2, 6],
	4 => [1 ,5 ,7],
	5 => [2, 4, 6, 8],
	6 => [3, 5, 9],
	7 => [4, 8],
	8 => [5, 7, 9],
	9 => [6, 8]
];

$pin = [];

for ($i = 0; $i < 6; $i++) {
	if ($i === 0) {
		$pin[] = rand(1, 9);
	} else {
		$last = $pin[$i - 1];
		$posibilities = $num[$last];
		$next = $posibilities[array_rand($posibilities)];
		$pin[] = $next;
	}
}

echo implode('', $pin) . PHP_EOL;