is prime, prime decomposition and totient functions

[johnmarinelli]

I made a PR a LOOOONG time ago and completely forgot to add tests, so it was closed - here is that same request with tests! Apologies for taking months...

[JoaoGFarias]

Great work @johnmarinelli, and sorry for taking months to reply.
Could you break the headers comments to a limit of 80 chars per line.
This way, is easier to read on GitHub or text editors.

[johnmarinelli]

No problem & will do.

[nryoung]

Thanks for your contribution.

A couple of things:

1. It is preferred to make a PR from a topic branch off of your master, please see: https://help.github.com/articles/using-pull-requests/
2. We also prefer to have a clean commit history, so if you could squash your commits and rebase off of master that would be ideal. Please see: https://github.com/edx/edx-platform/wiki/How-to-Rebase-a-Pull-Request as a guide.

Feel free to reopen with fixes.