gistfile1.txt

<?php

// PHP code to check whether a number is prime or Not
// function to check the number is Prime or Not
function primeCheck($number): int
{
    if ($number == 1)
        return 0;

    for ($i = 2; $i <= sqrt($number); $i++) {
        if ($number % $i == 0)
            return 0;
    }
    return 1;
}

function findPrimesRange($start, $finish): array
{
    // Initialise the range of numbers.
    $number = 2;
    $range = range(2, $finish);
    $primes = array_combine($range, $range);

    // Loop through the numbers and remove the multiples from the primes array.
    while ($number * $number < $finish) {
        for ($i = $number; $i <= $finish; $i += $number) {
            if ($i == $number) {
                continue;
            }
            unset($primes[$i]);
        }
        $number = next($primes);
    }

    // Slice the array into the given range
    foreach ($primes as $prime) {
        if ($prime < $start) {
            unset($primes[$prime]);
        } else {
            break;
        }
    }
    return $primes;
}

function test(): array
{
    $setOne = findPrimesRange(100, 1000);
    $setTwo = findPrimesRange(10, 100);
    $setThree = findPrimesRange(1000, 10000);

    $validNumbers = [];

    foreach ($setOne as $number) {
        $test = 1;
        foreach ($setTwo as $secondNumber) {
            foreach ($setThree as $thirdNumber) {
                $valid = intval(strval($number) . strval($secondNumber) . strval($thirdNumber));
                if (primeCheck($valid) == 1 && !isset($valid, $validNumbers)) {
                    array_push($validNumbers, $valid);
                }
            }
        }
    }
    return $validNumbers;
}