Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site othervax.UUCP Path: utzoo!linus!philabs!micomvax!othervax!pace From: pace@othervax.UUCP Newsgroups: net.math Subject: Yet Another Puzzle Message-ID: <313@othervax.UUCP> Date: Wed, 22-Aug-84 13:03:52 EDT Article-I.D.: othervax.313 Posted: Wed Aug 22 13:03:52 1984 Date-Received: Thu, 23-Aug-84 07:45:49 EDT Organization: Micom Co., Montreal Canada Lines: 29 (new improved bug killer...only $3.99 more) What we have here is a problem one of my lecturers back in the good old days gave me: Please forgive me if you've all seen this before but I havn't been reading net.math for very long. Anyway, here it is; for ANY POSITIVE integer, call it "i", will the following "program" ALWAYS (eventually!) stop ? step 1: if( i == 1 ) then STOP; step 2: if( i is even ) then i = i/2 else i = 3*i + 1; step 3: go to step 1; We do of course assume that 'i' can be infinitely large etc. Well, what do you think, can any of you give a proof showing that it will stop (or halt or exit, whatever) for any positive integer? You will probably immediately think of the old HALTING problem we all learned about back in school. Well, if you want to know whether it can be done or not (that's if you already havn't guessed it by now), drop me a line and I'll tell you. cheers , Scott Pace, Micom Co., Montreal