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Forum index » Science and Technology » Math » Recreational
primality preserving function?
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gsax
science forum beginner


Joined: 12 Jul 2005
Posts: 44

PostPosted: Sat Jul 16, 2005 3:44 am    Post subject: primality preserving function? Reply with quote
Hi

I was trying to come up with a function that is primality
preserving..i.e. let the function be f(x)...then I want

f(x) > x
&
f(x) is prime iff x is prime...

I have not been able to produce such a function...

I would like to know , if anyone has a example of such a function..

best regards
Gsax
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Gottfried Helms
science forum Guru


Joined: 24 Mar 2005
Posts: 301

PostPosted: Fri Jul 29, 2005 11:50 am    Post subject: Re: primality preserving function? Reply with quote
Jim Spriggs schrieb::
Quote:
gsax wrote:

Define formula.

Ok, so I have to define what I mean by a formula..!

well that is a tough one... but let me try to say that the formula
shall consist only of addition/subtraction, multiplication/division,
exponentiation...


Then I think your quest is a hopeless one. At present.


a bit out of seriousness... ;-)

f(x) = {log(x+1)/log(2) iff the result is a positive integer
{ 0 else


Gottfried Helms
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