Divisibility Tricks for 7

Normally, we are told that there are no convenient divisibility rules for division by $7$. This is actually not true. While there are no rules that are as elegant as the rules for for any other positive integer less than or equal to $12$, there are a couple of tricks that we can use in combination to test divisibility by $7$ in base-$10$. We describe and prove the validity of these rules in this video, and we provide concrete examples of their application.

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