Changing this will break all the solutions, and it's not really important here.

Appreciated, thanks :)

First point of the notes:

• The numbers are always positive.

Edit: also, your github account has a repo featured with kata solutions - please remove it or make it private (in bitbucket is for free), as you are not meant to share them.

It's meant to be very simple so I don't think there is any way to make this more interesting without changing the concept (i.e. using something besides math operations). You could make your own kata with a more intersting idea.

Glad you enjoyed. :)

Your Select-code didn't return anything... It was without effect.

Generally you are completely right: Changing a parameter is bad style. But in this kata it is part of the task, that is described .

A Select is not changing the Array/List, but it creates a new Enumerable. So you don't change anything.