21（二十一[er shi yi]）是20与22之间的自然数。是一个奇数、合数、半素数。

21用英文怎么写？

Twenty-one

英 [ˈtwenti wʌn]  美 [ˈtwenti wʌn]

Twenty-one的双语例句

1.We waited twenty-one years, don't fail us now. 

我们等了21年了，如今不要让我们失望。

2.I was twenty-two — no, twenty-one. 

我当时22岁，哎呀不对，是21岁。

3.Winterton has never had a sniff of a government job in his entire twenty-one years in parliament. 

在国会的整整21年里，温特顿没有得到过任何在政府里工作的机会。

4.He was stricken at twenty-one with a crippling malady. 

他21岁时突患致残重疾。

5.He said he was twenty-one years old and the employment agency took him on faith. 

他说他21岁，职业介绍所毫不怀疑就相信了他。