All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Numbers
Perpetual Primes Production? (Posted on 2006-11-29) Difficulty: 3 of 5
Pick a positive integer to start a sequence. Now double it, and add one to the result: this is the second number of your sequence. Double that number, and add one, and that will be your third number; repeat the doubling and adding, and you will have a fourth number, and so on.

If you start with a prime number, and you keep doubling and adding one, is it possible to produce a sequence with only prime numbers?

See The Solution Submitted by Old Original Oskar!    
Rating: 4.0000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
re: A bet | Comment 11 of 12 |
(In reply to A bet by Federico Kereki)

This conjecture is true for all primes through 8647. The verification program crashes with an overflow on the 8659th iteration of the doubling and adding for the next prime, 8663.

list
   10   N=2
   20   while Ct<48
   25   Lp=N
   30   N=nxtprm(N)
   35   Nu=N
   40   for I=1 to N-1
   50    Nu=2*Nu+1
   60   next
   70   if Nu @ N>0 then print N,Nu:Ct=Ct+1
   90   wend
OK
run
Overflow in 50
?lp
 8647
OK
?n
 8663
OK
?i
 8659
OK

Line 70 would have shown any exception to the rule.


  Posted by Charlie on 2006-11-30 09:07:59
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (1)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2017 by Animus Pactum Consulting. All rights reserved. Privacy Information