# Distribution of power congruence classes

1. Feb 22, 2012

### dec178

Hi, I need help to prove this for my professor
this is called "Distribution of power congruence classes" or something like that

With all n∈NiS∈N correct
1) n ≡Qs(n)(mod 10s-1)
2) n ≡Qs(n)(mod 10s+1)

2. Feb 23, 2012

### Stephen Tashi

You must explain your notation. What is $N_i$? What is $Q_s(n)$? What is $Q'_s(n)$ ?

Instead of "correct", perhaps you mean "it is true that".

3. Feb 23, 2012

### dec178

Yes, I need to proove, that this is correct.
To seperate $Q_s(n)$ and $Q'_s(n)$, I used apostrophe '
I dont know, professor just gave this for us in a middle of Modular arithmetic class

Last edited: Feb 23, 2012
4. Feb 23, 2012

### Norwegian

Can we perhaps decipher the question as follows:

Let n and s be positive integers, let Qs(n) be the sum of the numbers formed by the digits of n in groups of s, starting from the right, and let Qs'(n) be the alternating such sum.

Show that Qs(n)$\equiv$n (mod 10s-1) and Qs'(n)$\equiv$n (mod 10s+1)