string(285) "get document error：https://zhidao.baidu.com/search?lm=0&rn=10&pn=0&fr=search&dyTabStr=null&word=%E4%BB%80%E4%B9%88%E5%8F%AB%E5%81%9A%E8%87%AA%E7%84%B6%E6%95%B0%E7%9A%84%E5%AE%9A%E4%B9%89%E5%92%8C%E5%85%AC%E5%BC%8F => Failed to connect to 101.89.117.144 port 38017: Connection refused"
什么叫做自然数的定义和公式
