Playing time (1/2): When is a number divisible by 3? (Are you up for the challenge?)

At school, we learned that if the sum of its digits (cross sum) is divisible by 3, then the number itself is divisible by 3. A new method for Pros can be executed entirely mentally, leaving everyone astonished when you use this trick. It works regardless of the number's size. Here's a small example number, and it's possible to apply it to infinitely larger numbers: 73646229385734472654132980978732023023446763338576056857.

Manolo

Apr 9, 2025·Updated May 31, 2025·5 min read

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