function echoPrimeUpTo($range)
{
    echo "Printing prime numbers up tp {$range} <br>";
    for ($i = "1"; $i <= $range; $i++) {
        if (isPrime($i)) {
            echo "{$i}<br>";
        }
    }
}

function findPrimes($n)
{
    $primes = array();
    for ($i = 1; $i < $n; $i++) {
        if (isPrime($i)) {
            $primes[] = $i;
        }
    }
    return $primes;
}

function checkPrimeRange($start, $end)
{
    for ($i = $start; $i <= $end; $i++) {
        if (isPrime($i)) {
            echo "<strong>{$i}, </strong>";
        } else {
            echo $i . ", ";
        }
    }
}

function main()
{
    $max = 2000000;
    $sum = 0;
    foreach (range(1, $max) as $number) {
        if (isPrime($number)) {
            $sum += $number;
        }
    }
    echo $sum;
}

function tPrime($n)
{
    $len = strlen($n);
    for ($i = 2; $i <= $len; $i++) {
        if (isPrime(substr($n, 0, $i)) && isPrime(substr($n, strlen($n) - $i, $i))) {
        } else {
            return false;
        }
    }
    return true;
}

function countQuadraticConsecutivePrimes($a, $b)
{
    $nPrimes = 0;
    for ($n = 0; true; ++$n) {
        if (isPrime(abs($n * $n + $a * $n + $b))) {
            ++$nPrimes;
        } else {
            return $nPrimes;
        }
    }
}

function getPrimeNumbers($max)
{
    $result = '2';
    $nbr = 2;
    while ($nbr <= $max) {
        if ($nbr % 2 != 0) {
            if (isPrime($nbr)) {
                $result .= ',' . $nbr;
            }
        }
        $nbr++;
    }
    return $result;
}

function nextPrime($x)
{
    // Precondition: $x is prime or 1. (Handy for initialization of an iterator.)
    if ($x == 1) {
        return 2;
    }
    if (isDivisible($x, 2)) {
        --$x;
    }
    do {
        $x += 2;
    } while (!isPrime($x));
    return $x;
}

function main()
{
    $n = 10001;
    $number = 2;
    $i = 0;
    while (1) {
        if (isPrime($number)) {
            $i++;
            // echo $i . ' --  '. $number . PHP_EOL;
            if ($i === $n) {
                echo $number;
                break;
            }
        }
        $number++;
    }
}

function reducer($num, $sieve, $primes, $target)
{
    $negSieve = sieve($num, $primes);
    $new = $primes;
    foreach ($negSieve as $key => $value) {
        if ($value == 0 && isPrime($key, $primes)) {
            if (!in_array($key, $primes)) {
                $new[] = $key;
                if (count($new) - 1 == $target) {
                    result(104743, $new[$target - 1]);
                    die;
                }
            }
        }
    }
    return $new;
}

function factorize($number)
{
    $factors = array();
    if (isPrime($number)) {
        return array($number => 1);
    }
    $ceil = sqrt($number);
    $factor = 2;
    while ($factor <= $ceil) {
        if ($number % $factor == 0) {
            $factors = addFactorizations($factors, factorize($factor));
            $factors = addFactorizations($factors, factorize($number / $factor));
            break;
        }
        $factor++;
    }
    return $factors;
}

function isCircular($num)
{
    if (!isPrime($num)) {
        return false;
    }
    if ($num > 10) {
        $numstr = (string) $num;
        if (strstr($numstr, "0") || strstr($numstr, "5") || strstr($numstr, "2") || strstr($numstr, "4") || strstr($numstr, "6") || strstr($numstr, "8")) {
            return false;
        }
        $len = strlen($numstr);
        for ($i = 0; $i < $len - 1; $i++) {
            $numstr = (string) $num;
            $num = rotateLeft($numstr);
            if (!isPrime((int) $num)) {
                return false;
            }
        }
    }
    return true;
}

function factorize(&$target, &$primes, &$factor)
{
    $multiplier = 2;
    $factored = true;
    $sieve = range($primes[count($primes) - 1] + 1, $factor);
    for ($i = 0; $i < count($primes); $i++) {
        if ($target % $primes[$i] == 0) {
            $target = $target / $primes[$i];
            if (isPrime($target)) {
                result(6857, $target);
                die;
            }
        }
        if ($i == count($primes) - 1) {
            $factored = false;
            $factor *= $multiplier;
            $primes = reducer($factor, $sieve, $primes, $target);
            factorize($target, $primes, $factor);
        }
    }
}

<?php

/**
 * 10001st prime
 * https://projecteuler.net/problem=7
 */
require '../show_answer.php';
$startTime = microtime(true);
$number = 0;
$value = 2;
$max = 10001;
while ($number < $max) {
    if (isPrime($value)) {
        $number++;
    }
    $value++;
}
$result = $value - 1;
showAnswer($result, $startTime);
function isPrime($value)
{
    $root = sqrt($value);
    $divisor = 2;
    while ($divisor <= $root) {
        if ($value % $divisor == 0) {
            return false;
        }
        $divisor++;
    }
    return true;
}

    }
    return $prime ? true : false;
}
$text = "Hej. Idag är det ";
$text2 = "Tiden är ";
$today = date('Y-m-d');
$time = date("H:i:s");
$hemligSumma = array(10, 20, 30, 40, 50);
$slumpadSida = array('www.flashback.org', 'http://www.piratpartiet.se/', 'www.google.se', 'www.php.net');
echo $text . $today . "<br />" . $text2 . $time . "<br />";
echo "Idag skall vi räkna matematik: ";
if (isset($_POST['submit'])) {
    $summa = intval($_POST["ma1"]) + intval($_POST["ma2"]);
    echo $_POST["ma1"] . " + " . $_POST["ma2"] . " är lika med " . $summa . "<br /><br />";
    if ($summa == $hemligSumma[mt_rand(0, 4)]) {
        echo "Du lyckades hitta det hemliga nummret du får en länk <br />" . $slumpadSida[mt_rand(0, 3)];
    }
    echo isPrime($summa) ? $summa . ' är ett primtal<br/>' : $summa . ' är inte ett primtal<br/>';
}
?>
<form action="<?php 
echo $_SERVER['PHP_SELF'];
?>
" method="post">
<input type="text" name="ma1" /> +
<input type="text" name="ma2" /><br />
<input type="submit" name="submit" value="Räkna" />
</form>
</body>

</html>

<?php

function isPrime($num)
{
    if ($num == 1) {
        return false;
    }
    if ($num == 2) {
        return true;
    }
    if ($num % 2 == 0) {
        return false;
    }
    for ($i = 3; $i < $num; $i = $i + 2) {
        if ($num % $i == 0) {
            return false;
        }
    }
    return true;
}
$a = 127;
// для вывода числа
if (isPrime($a)) {
    echo "{$a} is a prime";
} else {
    echo "{$a} is not a prime";
}
echo "<br>";
var_dump(isPrime(127));
// булевым значением

            return false;
        }
    }
    return true;
}
function microtime_float()
{
    list($usec, $sec) = explode(" ", microtime());
    return (double) $usec + (double) $sec;
}
$start = microtime_float();
$startPrime = microtime_float();
$i = 0;
while ($i < 100000) {
    $rand = rand(1147483647, 2147483647);
    if (isPrime($rand)) {
        echo "+";
    } else {
        echo "-";
    }
    $i++;
}
$endPrime = microtime_float();
$startWrite = microtime_float();
$x = 0;
while ($x < 100) {
    $i = 0;
    $longString = '';
    while ($i < 10000) {
        $rand = rand();
        $longString .= $rand;

            return true;
        } else {
            for ($divisor = 2; $divisor <= (int) sqrt($num); $divisor++) {
                if ($num % $divisor == 0) {
                    return false;
                }
            }
        }
    }
    return true;
}
if (isset($_POST['submit']) && $_POST['start'] != '' && $_POST['end'] != '' && is_numeric($_POST['start']) && is_numeric($_POST['end'])) {
    $start = $_POST['start'];
    $end = $_POST['end'];
    for ($i = $start; $i <= $end; $i++) {
        if (isPrime($i)) {
            ?>
                    <strong><?php 
            echo $i;
            ?>
</strong>
                <?php 
        } else {
            echo $i;
        }
        if ($i != $end) {
            echo ", ";
        }
    }
}
?>

<?php

require_once '../functions.php';
$num = 2;
$i = 0;
while (true) {
    if (isPrime($num)) {
        $i++;
    }
    if ($i == 10001) {
        break;
    }
    $num++;
}
echo $num;

<?php

$fp = fopen("php://stdin", "r");
$testCases = 0;
fscanf($fp, "%d", $testCases);
$n = 0;
while ($testCases-- > 0) {
    fscanf($fp, "%d", $n);
    echo isPrime($n), "\n";
}
function isPrime($n)
{
    if ($n === 1) {
        return "Not prime ";
    }
    for ($i = 2; $i * $i <= $n; ++$i) {
        if ($n % $i === 0) {
            return "Not prime";
        }
    }
    return "Prime";
}