IBM Research | Ponder This | May 2004 challenges
Skip to main content

Ponder This

May 2004

<<April May June>>

Ponder This Challenge:

This month's puzzle evolved from a suggestion of Michael Brand.
It is a twist on Edouard Lucas' "Towers of Hanoi" puzzle.

To be considered for publication, please supply answers for BOTH parts of the puzzle.

Part 1:
There are three pegs, labelled "A", "B", "C"; and 64 disks of different sizes, numbered from 1 (smallest) to 64 (largest). At no time does a larger disk sit atop a smaller one. We are allowed to move disks, one at a time, from peg to peg, as long as this size rule is obeyed.

When we first see these pegs, "A" has 35 disks, "B" has 18, and "C" has 11. A card next to the pegs indicates that the minimum number of moves required to move all disks to one peg is 3141592653589793238. What disks are on "C", and what disks are on "B"? (The answer is not unique.)

Please submit your answer in a plaintext message (no attachments) in the following format:

C: 2,5,22,23,24,29,30,34,36,40,59
B: 1,3,6,7,8,9,11,14,15,18,19,31,35,43,48,49,51,56

recalling that "1" is the smallest disk.
(The commas may be replaced by spaces.)

Part 2:
A computer program is used to move all 64 disks from peg A to peg B in the fastest route. After several iterations, someone stops the program. The program displays, after every step, the identity of the top disk on each of the three pegs (overwriting the old values as it does so), so, after the program stopped, all you can see is the current state of these. Is this enough information in order for you to determine what the next move should have been? Prove your claim.

As usual, each answer is expected to be your own work.
Computer assistance is allowed, but the answer can be attained by hand.

We will post the names of those who submit a correct, original solution! If you don't want your name posted then please include such a statement in your submission!

We invite visitors to our website to submit an elegant solution. Send your submission to the

If you have any problems you think we might enjoy, please send them in. All replies should be sent to:


Challenge: 05/01/2004 @ 9:30 AM ET
Solution: 06/01/2004 @ 8:30 AM ET
List Updated: 05/10/2004 @ 1:30 PM ET

People who answered correctly:

Eugene Vasilchenko (5.03.2004 @08:55:45 PM EDT)
IQSTAR (5.04.2004 @01:15:07 PM EDT)
Hagen von Eitzen (5.05.2004 @05:00:40 AM EDT)
Rocke Vesser (5.05.2004 @10:38:42 AM EDT)
Coserea Gheorghe (5.05.2004 @11:39:31 AM EDT)
Joe BGI S Fendel (5.05.2004 @12:17:36 PM EDT)
Michael Peeters (5.05.2004 @08:15:06 PM EDT)
Bart De Vylder (5.06.2004 @04:53:28 AM EDT)
Christopher Howe (5.06.2004 @12:41:33 AM EDT)
Sorin Ostafiev (5.07.2004 @03:43:37 PM EDT)
Dave Blackston (5.07.2004 @05:24:37 PM EDT)
Patrick J. LoPresti (5.08.2004 @10:15:47 PM EDT)
Daniel Bitin (5.10.2004 @05:55:57 AM EDT)
Siva Dirisala (5.10.2004 @02:51:13 PM EDT)
John Ritson (5.11.2004 @07:41:15 AM EDT)
Frank Mullin (5.11.2004 @10:00:17 AM EDT)
Olivier Miakinen (5.11.2004 @06:08:32 PM EDT)
Dharmadeep Muppalla (5.12.2004 @02:55:32 AM EDT)
John G. Fletcher (5.13.2004 @12:44:31 AM EDT)
Brad Austin (5.13.2004 @06:53:48 PM EDT)
Karl D'Souza (5.17.2004 @09:45:00 AM EDT)
Dan Dima (5.20.2004 @11:07:17 AM EDT)
Aditya K Prasad (5.21.2004 @10:59:00 AM EDT)
Syed Atif Hussain (5.26.2004 @05:35:31 AM EDT)
David McQuillan (5.26.2004 @05:08:50 PM EDT)
Wolfgang Kais (5.27.2004 @02:43:10 AM EDT)
Kunal Shroff (5.28.2004 @05:03:00 PM EDT)

Attention: If your name is posted here and you wish it removed please send email to the