Re: Re: Finding a relative prime

*To*: mathgroup at smc.vnet.net*Subject*: [mg19757] Re: [mg19704] Re: Finding a relative prime*From*: "Frans Martens" <fransm at win.tue.nl>*Date*: Wed, 15 Sep 1999 03:53:06 -0400*Reply-to*: fransm at win.tue.nl*Sender*: owner-wri-mathgroup at wolfram.com

Hello, Timur Tabi wrote I'm using Mathematica 3.0 for the Mac, and I'm trying to figure out how to get it to pick a random number that is relatively prime to another number, p-1, where p is prime. In other words, pick a random number k such that 1) k is between 2 and p-1, and 2) k is relatively prime to p-1. How can I do that in Mathematica 3.0? Ken Levasseur used in his solution FixedPoint. relprime[p_] := FixedPoint[Random[Integer, {2, p - 2}] &, p - 1, SameTest -> ((GCD[p - 1, #2] == 1) &)] You can also use a recursive function: Clear[f]; f[p_] /; PrimeQ[p] && p > 3 := (If[GCD[#1, p - 1] === 1, #1, f[p]] & )[Random[Integer, {2, p - 2}]] Frans Martens Eindhoven University of Technology Faculty of Mathematics and Computer Science P.O.Box 513 5600 MB Eindhoven The Netherlands Telephone -31402474280 Telefax -31402436685 E-mail fransm at win.tue.nl