What is the formula to determine how many cubes are on the surface of
a rubics cube. Or, what is the formula for finding the number of cubes
on the inside of a rubic cube. Ex a 3x3 cube has 27 sub-cubes. 26 are
on the outside, 1 inside. How do you figure this out for a 5x5, 9x9,
etc...

Hello.

The formula is quite simple:

(n-2)^3 
where 'n' is the length/width of the exterior cube.

source:
"Consider the "inner" cube, i.e. the cube formed by the small cubes 
that are not on the faces on the large cube. The size of the edge of 
the inner cube is (n-2), and it contains (n-2)^3 small cubes."
From Mathforum.org
http://mathforum.org/library/drmath/view/62272.html

so:

For 3x3, n=3
(3-2)^3 = 1^3 = 3

For 5x5, n=5
(5-2)^3 = 3^3 = 27

For 9x9, n=9
(9-2)^3 = 7^3 = 343

source: Google calculator:
://www.google.com/search?hl=en&ie=ISO-8859-1&q=%289-2%29%5E3&btnG=Google+Search

------
search strategy:
"n-2" "interior cube"

I hope this helps.

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Clarification of Answer by juggler-ga on 17 Sep 2004 10:45 PDT

Sorry for that typo above:

Obviously:
For 3x3, n=3
(3-2)^3 = 1^3 = 1