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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
This is indeed correct, thanks for noticing! I've amended my code to recognise 1 as not prime and include 4 in the prime checks. This is submitted as a new solution here:
https://www.codewars.com/kata/reviews/561eaaf5353ce442ad00004d/groups/5b43601cff888b9e620030d6
Unfortunately, I don't know how to change this particular code here...