IBM Ponder This #162 · October 2011

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.

Solution

Best opened after a real attempt

To be added.