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

means

> 
> I *just* can't remember the/this telephone number.
> 
> 
>