Jquery gets the number of the same child under an element

For example, in the following HTML code, to get the number of a elements below the P element:

<p id="father"> 
<a></a> 
<a></a> 
<a></a> 
<a></a> 
<a></a> 
 ...  
<a></a> 
</p> 

We can write it like this:

$("#father a").length