public function getNumberDescendants()
	{
		$intervalSize = $this->getIntervalSize();
		$intervalSize = $intervalSize - 1;
		
		if ($intervalSize % 2 != 0) {
			$dump = static::dump($this);
			throw new Exception\InvalidStructure("The size of node {$dump} must be odd number, even number received");
		}
		$descendantCount = (int) ($intervalSize / 2);
		
		return $descendantCount;
	}