Question: I’ve almost never encountered the word *einfallen* before, so it’s no wonder I don’t understand its meaning in the sentence:

> 
> Mir fällt die Telefonnummer einfach nicht ein.
> 
> 
> 

Dictionaries do everything they can to make the meaning of the sentence yet even more obscure, supplying me with translations like:

> 
> The telephone number doesn’t occur to me easily.  
> 
>  The telphone number doesn’t come to me easily (Probably in the sense of *sich erinnern an*).  
> 
>  The telephone number doesn’t collapse/invade (and does all other things, it's famous for)
> 
> 
>

Answer: 
*Einfallen* has a lot of meanings in German (see [dict.cc](http://www.dict.cc/?s=einfallen)). This is why the translator is a bit confused.

In your case it would be

> 
> to cross sb.'s mind  
> 
>  to come into sb.'s mind / head  
> 
>  to occur to sb.
> 
> 
> 

I would translate your sentence as follows:

> 
> The telephone number doesn’t come into my mind.
> 
> 
>
I would translate "einfallen" as "come to mind," or to remember.

The literal translation is to "fall into."

But a thought has to "fall into" something.

That "something" is one's mind.