Regular verification of ID number

 if (!checkCertNo($input['certNo'])) {
    
            echo " The ID number is incorrect. ";
        }

function checkCertNo($idcard)
{
    
    $len = strlen($idcard);
    if ($len != 18) {
    
        return false;
    }
    $idcard_base = substr($idcard, 0, 17);
    // Weighting factors 
    $factor = [7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2];
    // Check code corresponding value 
    $verify_number_list = ['1', '0', 'X', '9', '8', '7', '6', '5', '4', '3', '2'];
    $checksum = 0;
    for ($i = 0; $i < strlen($idcard_base); $i++) {
    
        $checksum += substr($idcard_base, $i, 1) * $factor[$i];
    }
    $mod = $checksum % 11;
    return strtoupper(substr($idcard, 17, 1)) == $verify_number_list[$mod];
}