Question

How to check whether a given number is a twisted prime number in PHP

Answer 1

function reverseNumber($n) {
    $reverse = 0;

    while ($n != 0) {
        $reminder = $n % 10;
        $reverse = $reverse * 10 + $reminder;
        $n = (int)($n / 10);
    }
    return $reverse;
}
 
function isPrime($n) {
    if ($n < 2 || ($n % 2 == 0 && $n != 2)) {
        return 0;
    }
 
    $count = floor(sqrt($n));
    for ($i = 3; $i <= $count; $i += 2) {
        if ($n % $i == 0) {
            return 0;
        }
    }
    return 1;
}

    
$n = 79;
$reverse_n = reverseNumber($n);

if (isPrime($n) && isPrime($reverse_n)) {
    echo "Twisted prime number\n";
} else {
    echo "Not twisted prime number\n";
}




/*
run:
 
Twisted prime number
 
*/

 

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