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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.
There is an O(1) time solution. Took me a while to find it out... Good luck ;)
math.isqrtThe error says you run into a stack overflow. Most probably your recursion is too deep and exhausts stack space.