[net.math] resistor cube and N dim cubes

az@ada-uts.UUCP (10/30/85)

   The only formula for n-dimensional cube I could find is:
	the sum for k from 0 to (n-1) of k!(n-k-1)!/n!
(I could not simplify it any further.)

   A sketchy proof: for any given k (0<=k<=n) the cube has
n!/(k!(n-k)!) of vertices which are k edges from the "leftmost" vertex.
Let's call this vetices k-vertices. There are (n-k) edges going from any
given k-vertex to k+1-vertex. After we merge equipotential vertices,
corresponding "bunch" has resistence (k!(n-k-1)!/n! Ohm.

Just in case anybody is interested, first 40 values follow:

n=1, r=1	  n=11, r=.206782   n=21, r=.100616   n=31, r=.066834
n=2, r=1	  n=12, r=.186724   n=22, r=.095762   n=32, r=.064667
n=3, r=.833333	  n=13, r=.170285   n=23, r=.091359   n=33, r=.062636
n=4, r=.666667	  n=14, r=.156571   n=24, r=.087346   n=34, r=.06073
n=5, r=.533333	  n=15, r=.144952   n=25, r=.083673   n=35, r=.058936
n=6, r=.433333	  n=16, r=.134976   n=26, r=.080298   n=36, r=.057246
n=7, r=.359524	  n=17, r=.126311   n=27, r=.077186   n=37, r=.05565
n=8, r=.304762	  n=18, r=.118711   n=28, r=.074307   n=38, r=.054141
n=9, r=.263492	  n=19, r=.111987   n=29, r=.071636   n=39, r=.052711
n=10, r=.231746	  n=20, r=.105993   n=30, r=.069151   n=40, r=.051356

Alex Zatsman, Intermetrics,Inc., Cambridge, Mass.