I intended the simplest form of this problem,
and must have muddled my intent. In regard
to the issue of rotational symmetry, I just
meant that if you can rotate a "mountain"
thru a quarter or half turn and get the same
result, it should only be counted once. I
should probably have left the condition out.
As to vertical gaps, except for the bottom layer,
which must be full of cubes, every cube must
be situated over a column of cubes (no gaps
vertically) but within a layer any configuration
is allowed (so placing cubes in opposite corners,
creating "horizontal" gaps, is fine.)
Sorry about any confusion.
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