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All 1's (Posted on 2013-12-14) Difficulty: 3 of 5
(1) Find a test for divisibility by 111.

(2) Extending this, find a test for divisibility by any number consisting solely of 1's.

Please explain why your tests work.

No Solution Yet Submitted by Danish Ahmed Khan    
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re: Divide and conquer (spoiler) & a challenge | Comment 2 of 3 |
(In reply to Divide and conquer (spoiler) by Steve Herman)

Great solution, however I was hoping someone would come up with an elegantly simple method that can be done "in one's head", along the lines of the divisible by 3 and/or 9 that most of us know.  I grew up in the era before PCs and calculators, and these rules were extremely useful, almost necessary, then.

Who's up to the challenge?

  Posted by Kenny M on 2013-12-15 10:09:52

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