Question

How to find the sum of all the primes below two million in PHP

Answer 1

function isPrime($n) {
    if ($n < 2 || ($n % 2 == 0 && $n != 2)) {
        return false;
    }
  
    $count = floor(sqrt($n));
    for ($i = 3; $i <= $count; $i += 2) {
        if ($n % $i == 0) {
            return false;
        }
    }
    return true;
}

$num = 2000000;
$sum = 0;

for ($i = 2; $i < $num; $i++) {
    if (isPrime($i)) {
        $sum += $i;
    }
}

echo "sum = " . $sum;




/*
run:

sum = 142913828922

*/

 

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