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  • Question : Prove that the number alt text is never divisible by 5.
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    Why those tags?2011-01-04
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    A hint (although I haven't tried this in detail): call this number $f(n)$. Then $f(n)$ might satisfy some linear recurrence. Plug integers mod 5 into this recurrence and see what happens.2011-01-04
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    @Michael Lugo, Yup, that approach works.2011-01-04
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    f(n) _has to_ satisfy a linear recurrence, but there are easier ways to do this problem. Again, what have you tried?2011-01-04

3 Answers 3