IBM Research | Ponder This | October 2011 challenges

# Ponder This

## October 2011

<<September October November>>

Ponder This Challenge:

We call a real number R "interesting" if the product of every 8 consecutive decimal digits is 40,320.

Build a network from no more than twenty 1-ohm resistors such that their overall resistance, see (external link http://en.wikipedia.org/wiki/Series_and_parallel_circuits for details) R would be interesting.

Please submit your answer as pairs of letters, in which each pair represents the endpoints of a resistor, where the overall resistance is measured between "a" and "z".

For example, the following network is a cube, measured along the long diagonal: "ab bc cd da ef fz zh he ae bf cz dh".

We know that atto-ohm accuracy is meaningless, but this is a mathematical challenge, not an electrical engineering one.

Hint: This month's challenge can be solved on the back of an envelope.

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 ponder@il.ibm.com.

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

Challenge: 10/01/2011 @ 10:00 AM EST
Solution: 11/01/2011 @ 10:00 AM EST
List Updated: 10/01/2011 @ 10:00 AM EST

Jan Fricke (09/30/2011 08:32 PM EDT)
János Kramár (10/01/2011 12:22 AM EDT)
Yuanmi Chen (10/01/2011 08:27 AM EDT)
Alan Murray (10/01/2011 11:44 AM EDT)
Dan Dima (10/01/2011 12:54 PM EDT)
Leif Jensen (10/01/2011 01:22 PM EDT)
Pei Wu (10/02/2011 11:17 AM EDT)
Lu Wang (10/02/2011 12:04 AM EDT)
Piet Orye (10/02/2011 06:00 AM EDT)
Peter Gerritson (10/02/2011 07:26 PM EDT)
Ariel Flat (10/02/2011 08:19 PM EDT)
Arthur Breitman (10/03/2011 12:36 PM EDT)
Harold Gutch & Stefan Zehl (10/03/2011 01:15 PM EDT)
William Mantzel (10/03/2011 02:00 PM EDT)
Andreas Razen (10/03/2011 03:08 PM EDT)
Radu-Alexandru Todor (10/03/2011 07:21 PM EDT)
Chuck Carroll (10/03/2011 08:05 PM EDT)
Avishalom Shalit (10/04/2011 11:33 AM EDT)
Chris Kuklewicz (10/04/2011 04:58 PM EDT)
Adam Daire (10/04/2011 07:04 PM EDT)
Victor Chang (10/04/2011 08:49 PM EDT)
Josh Small (10/06/2011 11:54 AM EDT)
Ken Bateman (10/06/2011 02:40 PM EDT)
Shilei Zang (10/06/2011 03:46 PM EDT)
Yasodhar Patnaik (10/07/2011 03:26 AM EDT)
Gary M. Gerken (10/08/2011 08:01 PM EDT)
Renato Fonseca (10/09/2011 03:19 PM EDT)
David Greer (10/10/2011 07:45 AM EDT)
John Tromp (10/10/2011 12:50 PM EDT)
Maohua Sheng (10/10/2011 12:52 PM EDT)
Daniel Bitin (10/11/2011 11:07 AM EDT)
Phil Muhm (10/11/2011 02:53 PM EDT)
Armin Krauss (10/11/2011 03:14 PM EDT)
Liubing Yu (10/11/2011 06:30 PM EDT)
Adrian Neacsu (10/12/2011 04:21 PM EDT)
Hamidreza Bidar (10/12/2011 06:15 PM EDT)
Clive Tong (10/13/2011 05:09 PM EDT)
Movin Jain (10/14/2011 01:26 PM EDT)
Joseph DeVincentis (10/14/2011 10:08 PM EDT)
Pritibhushan Sinha (10/15/2011 04:48 AM EDT)
Peter de Rivaz (10/15/2011 04:59 AM EDT)
Dejan Stakic (10/16/2011 06:46 AM EDT)
David Friedman (10/16/2011 11:05 AM EDT)
Manoj vedvistara (10/16/2011 01:23 PM EDT)
Harald Bögeholz (10/16/2011 03:17 PM EDT)
Jeff Steele (10/17/2011 03:06 PM EDT)
Kipp Johnson & Nick Vigo (10/18/2011 11:58 AM EDT)
Tom Sirgedas (10/18/2011 08:45 PM EDT)
Chris Shannon (10/19/2011 01:04 AM EDT)
Jan Braunisch (10/19/2011 02:51 AM EDT)
Dr. Beena George (10/19/2011 05:02 AM EDT)
Stéphane Higueret (10/20/2011 10:07 PM EDT)
Franza Cavalcante Jr (10/21/2011 03:20 PM EDT)
Haoyu Bai (10/25/2011 01:01 AM EDT)
Thomas Rohr (10/26/2011 05:19 AM EDT)
Mathias Schenker (10/27/2011 11:10 AM EDT)
Yuan Yuan (10/28/2011 11:42 PM EDT)
Frederik Kaster (10/31/2011 03:02 PM EDT)

Attention: If your name is posted here and you wish it removed please send email to the ponder@il.ibm.com.