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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.
Please use spoiler flag when you give clues to a solution, even if they seem bad. This is a 4 kyu kata, so some efficiency is required and brute force won´t pass, whatever the way you do it. I don't see how to help you without spoiling. You have to think and try out considering the number and the digits that form it.