code: public function isPrime()
      {
          if ($this->value < 2) {
              return false;
          }
  
          if ($this->value === 2) {
              return true;
          }
  
          if ($this->isEven()) {
              return false;
          }
  
          for ($i = 3; $i <= ceil(sqrt($this->value)); $i = $i + 2) {
              if ($this->value % $i == 0) {
                  return false;
              }
          }
  
          return true;
      }
docs: Is this a prime?
  
  @return boolean