• darkpanda@lemmy.ca
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    13 hours ago

    If all of the digits summed recursively reduce to a 9, then the number is divisible by 9 and also by 3.

    If the difference between the sums of alternating sets digits in a number is divisible by 11, then the number itself is divisible by 11.

    That’s all I can remember, but yay for math right?