This is a programming kata I designed and used in a Coding Dojo held at University.
The Code

The problem and the base code was programmed by me, and includes step-by-step refactors. It's published in github in this link.
The Coding Dojo

Here's the announce in my blog:
Kata Euler
Published:

Kata Euler

Code Kata to teach some refactoring with TDD

Published:

Creative Fields