I'm going to Hell for this

10001.php

<?php

$position = 10001;

$primes = [ 2 => 2 ];
$miscreants = [ 1 => 1 ];

$x = $n = 2;
$target = $frame = ($position * 5);
$base = 0;

$g = true;

while (true) {
    if ($x <= $target) {
        $right = $x + 1;
        
        if (!isset($miscreants[$right]) && $right <= $target) {
            $primes[$right] = $right;
        }

        if (!$g) {
            if (isset($primes[$x])) {
                unset($primes[$x]);
            }
        } else {
        }
        
        $miscreants[$x] = $x;
    }
    
    if ($x >= $target) {
        ++$n;
        
        if ($n >= $target) {
            if (count($primes) >= $position) {
                break;
            }
            
            $base = $target;
            $n = 2;
            $target += $frame;
        } else {
        }
        
        $g = ($n > $base);
        
        $m = $base ? ($base - ($base % $n)) : 0;
        
        $x = $m + $n;
    } else {
        $x += $n;

        $g = false;
    }
}

$prime = array_slice($primes, $position - 1, 1);

echo $prime[0];