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* in this context is closely related to *erinnern*. While *sich an etwas erinnern* is a conscious process where the subject is the person *remembering* and thus the verb is best translated by *to remember something*, in the case of *einfallen* it is more an appearing idea — and the idea is also the subject.

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

is equivalent to, but syntactically distinctly different from:

> 
> Ich erinnere mich nicht an die Telefonnummer.
> 
> 
> 

Both would best be translated into the same English sentence:

> 
> I can’t/don’t remember the telephone number.
> 
> 
> 

The difference is a slight nuance. When saying »Sie fällt mir nicht ein«, you are just waiting for the helpful spark of a thought and then it should be there. When saying »ich erinnere mich nicht an sie«, you’re trying to remember but can’t make it happen.

And note how the *einfallen* or *(hin)einfallen* figuratively alludes to an idea dropping into your head — much like the other meanings of *einfallen* (to invade, to collapse, etc.).

---

Here are some examples on the other meanings of that verb, which could be the reason for it being confusing. First, in the sense of *invading*:

> 
> Heute Nacht wird unsere Armee in das Nachbarland einfallen.  
> 
> Tonight our army will invade the neighboring country.
> 
> 
> Letztes Jahr fielen die wilden Horden in unser Land ein.  
> 
> Last year the wild masses invaded our country.
> 
> 
> 

Documented on [dict.cc](http://www.dict.cc/?s=in+etw+einfallen+%5BGebiet+Land+etc+%5D).

And, second, an example in the sense of *collapsing*:

> 
> Gestern Nacht ist die alte Scheune eingefallen.  
> 
> Yesterday night the old barn collapsed.
> 
> 
>
*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.
> 
> 
>