I'm thinking of a 10 digit number that uses the each digit 0 to 9 exactly once and where the number formed by the first n digits is divisible by n. What could my number be? The video explains how to find the answer using tests for divisibility.
Blog post: http://wp.me/p6aMk-4yS
Divisibility by 7 graph: https://www.youtube.com/watch?v=vxHrfIom-YA
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