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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.
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Why is the estimated rank 3kyu
A duplicate of
https://www.codewars.com/kata/perfect-number-verifier
(Also, serious lack of tests and no random tests)