| Neighbors of a cell are only considered in the X and Y directions.
Number of ways to dig an n X n hole where each cell is at a different depth and water will collect in just one puddle.
Computed using a C program, brute force enumeration except using a cache of old results to cut off the search tree. For many related problems however, R. H. Hardin has coded them in S/R (which is COSPAN's language).
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