Hi !

I've got a little problem, seems simple... Here it is :

Text :

We're going to study all couples (n,k) such as :

Question :

Let and . Also

Show that

So far... :

By replacing the combinations with their formulas with !, i've found that :

So it's easy to show that

And now... ?

I can't find how to show that or :'(

I thought Bézout's identity could help, but no...

Thanks in advance !