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- Newsgroups: sci.math
- Subject: Re: Summer Problems
- Message-ID: <a_rubin.715552566@dn66>
- From: a_rubin@dsg4.dse.beckman.com (Arthur Rubin)
- Date: 3 Sep 92 20:36:06 GMT
- References: <1992Sep2.104741.12452@greco-prog.fr>
- Nntp-Posting-Host: dn66.dse.beckman.com
- Lines: 27
-
- In <1992Sep2.104741.12452@greco-prog.fr> loeb@greco-prog.fr (Daniel LOEB) writes:
-
- >(DMITRI) - A door has a very strange lock. It contains n holes
- >arranged in a regular polygon. There are buttons at the bottom of the
- >holes. When all buttons are up or all down, the door opens. Buttons
- >can only be examined or changed by sticking your arms in the holes.
- >When your arms are removed from the holes, the lock spins very quickly
- >and then stops at an unknown point. How many hands h(n) must you have
- >in order to be SURE to open the doors after a finite number of
- >manipulations.
- >Partial results: if p is prime, then h(p)=p-1. Otherwise, h(4)=2 and
- >h(1)=0.
- >Is there a general rule? Generalizations?
-
- h(n) = n(1-1/p), where p is the largest "prime" divisor of n (prime including
- 1, to handle h(1)=0). I think I've seen this problem before; probably in
- the American Mathematical Monthly or Mathematics Magazine, both published
- by the Mathematical Association of America. I think I see a fairly
- straightforward proof that that number is sufficient; I don't see how to
- proof necessity at the moment.
-
- Standard disclaimers apply.
- --
- Arthur L. Rubin: a_rubin@dsg4.dse.beckman.com (work) Beckman Instruments/Brea
- 216-5888@mcimail.com 70707.453@compuserve.com arthur@pnet01.cts.com (personal)
- My opinions are my own, and do not represent those of my employer.
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-