code: protected function pageNumberToKey($pageNumber)
      {
          if (isset($this->pagination[CanvasPageLink::CURRENT])) {
              return ($pageNumber - 1) * $this->pagination[CanvasPageLink::CURRENT]->getPerPage();
          }
          return false;
      }
docs: Convert a page number to an array key
  
  @param int $pageNumber 1-indexed page number
  
  @return int|false