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A331507
Water retention for an n X n number square with the maximum number of ponds using a simple filling pattern.
1
0, 0, 1, 5, 30, 74, 195, 363, 700, 1124, 1845
OFFSET
1,4
COMMENTS
The number placement starts with the lowest available number and proceeds from top left to bottom right in two separate passes. The first pass fills in the ponds. The second pass fills in the barrier cells surrounding the ponds.
A number square contains each of the numbers 1 to n*n exactly once.
The water retention model provides the definition of a pond. All the ponds have an area of 1 cell in the maximum pond example.
The immediate environment of a 1-cell pond requires four larger surrounding cells. The water retention model requires the macro environment of possible surrounding cells to be lower than the border of the 1-cell-area pond.
For even-ordered squares one of the main diagonals is made up of ponds. For odd-ordered squares both diagonals are made up of ponds.
The cells in a given row hold identical amounts of water.
A listing of the C code that calculates the water retention is given. The program gives a graphic output where the area of the ponds is color coded. Additional 3D graphics and other water retention utilites are available on Harry White's web page noted below.
The water retention model functions in three dimensions as noted in the crossrefs. The physical interpretation in three dimensions is not straightforward and the term "incarceration" of numbers is introduced.
EXAMPLE
Order 5 square retaining 30 units of water. The positions of the remaining numbers that do not occupy the pond cells or their immediate borders are irrelevant and a zero is placed in these positions.
0 6 0 7 0
8 1 9 2 10
0 11 3 12 0
13 4 14 5 15
0 16 0 17 0
CROSSREFS
Cf. A201126 (water retention on magic squares), A261347 (water retention on number squares), A275359 (3 dimensional incarceration), A275339.
Sequence in context: A043886 A044463 A270811 * A152745 A187275 A344070
KEYWORD
nonn,more
AUTHOR
Craig Knecht, Jan 18 2020
STATUS
approved