Given Constraints

// Constraints
// 1 <= keys[i] <= 2.5 * 10^13

Minimum value will be 1 &
Maximum value will be 25,000,000,000,000

Sample 1
Given array of n numbers.
[100, 15, 30, 10]

need to find the all numbers (between 1 to each number given in array) who has exactly 3 divisors.

For example
given number is 10
so need to find all the numbers from 1 to 10 who has exactly 3 divisors.
From 1 to 10:
• 4 (the three divisors are 1, 2 & 4)
• 9 (the three divisors are 1, 3 & 9)
so we will return 2 (count). Because 4 & 9 are 2 numbers who exactly have 3 divisors.

So the answer of the sample 1 is
[4, 2, 3, 2]
Explanation

• 100 has exactly 4 numbers (4, 9, 25, 49)….
• 15 has exactly 2 numbers (4, 9)….
• 30 has exactly 2 numbers (4, 9, 25)….
• 10 has exactly 2 numbers (4, 9)….

so far we found that all the numbers are square of prime numbers
• like 4 is a square of 2 & 2 is a prime number
• 9 is a square of 3 & 3 is a prime number
• 25 is a square of 5 & 5 is a prime number
• 49 is a square of 7 & 7 is a prime number

function arrayOfDivisors($x) {
    $result = [];
    for ($i = 1; $i <= $x; $i++) {
        $divisors = 0;
        for ($j = 1; $j <= $i; $j++) {
            if ($i % $j == 0) {
                $divisors++;
            }
        }
        if ($divisors == 3) {
            $result[] = $i;
        }
    }
    return $result;
}

function square_of_primes($limit) {
    $result = array();
    for ($i = 2; $i * $i < $limit; $i++) {
        $is_prime = true;
        for ($j = 2; $j * $j <= $i; $j++) {
            if ($i % $j === 0) {
                $is_prime = false;
                break;
            }
        }
        if ($is_prime) {
            $result[] = $i * $i;
        }
    }
    return count($result);
}

function findDivisors($arr) {
    $result = [];
    foreach ($arr as $num) {
        $result[] = square_of_primes($num);
    }
    return $result;
}


$arr = [100,10, 30];
$divisors = findDivisors($arr);
echo "<pre>";
print_r( $divisors );