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A336659
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a(n) is the maximal number of 1 X 1 squares in an arrangement of n squares, from 1 X 1 to n X n, where the squares are inside the n X n square.
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4
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1, 1, 2, 4, 8, 10, 15, 22, 28, 34, 41, 52, 60, 70, 83
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OFFSET
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1,3
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COMMENTS
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Note that distinct arrangements could give the same result for some values of n.
Up to rotation and reflection, the solutions for n=8 and n=9 shown in the examples are unique. There are 4 solutions corresponding to a(10)=34, 12 for a(11)=41 and 8 for a(12)=52. See Rosenthal links. - Hugo Pfoertner, Aug 04 2020
Lower bounds for the next terms are a(14)>=70, a(15)>=83, a(16)>=93, a(17)>=107, a(18)>=121, a(19)>=136, a(20)>=153 (from Hermann Jurksch, private communication). - Hugo Pfoertner, Aug 30 2020
More lower bounds a(21)>=168, a(22)>=187, a(23)>=206, a(24)>=222, a(25)>=242 (from Hermann Jurksch, private communication). - Rainer Rosenthal, Oct 07 2020
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REFERENCES
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Rodolfo Kurchan, Mesmerizing Math Puzzles, Sterling Publications, (2000), problem 87, Square Stamps, p. 57.
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LINKS
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Rodolfo Kurchan, Problem 577, Puzzle Fun, December 1997.
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EXAMPLE
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Consider the first quadrant of the square grid.
For n = 1 we draw a 1 X 1 square, so a(1) = 1.
For n = 2 we draw a 2 X 2 square and then we draw a 1 X 1 square, both with a vertex at the point (0,0) as shown below:
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We can see only one 1 X 1 square in the arrangement, so a(2) = 1.
For n = 3 first we draw a 3 X 3 square and then we draw a 2 X 2 square, both with a vertex at the point (0,0) as shown below:
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Finally we draw a 1 X 1 square on the cell (3,2) as shown below:
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| |_| <-- cell (3,2)
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Note that below the cell (3,2), on the cell (3,1), we have formed a new 1 X 1 square, hence the total number of 1 X 1 squares in the arrangement is equal to 2, so a(3) = 2. (End)
Based on exhaustive enumeration by Hermann Jurksch, the following arrangements of squares are examples of optimal solutions:
a(8) = 22
side lower left vertex
1 (7, 7)
2 (6, 3)
3 (5, 1)
4 (4, 2)
5 (1, 3)
6 (0, 0)
7 (0, 0)
8 (0, 0)
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a(9) = 28
side lower left vertex
1 (0, 6)
2 (1, 7)
3 (1, 3)
4 (0, 5)
5 (0, 4)
6 (3, 1)
7 (2, 2)
8 (0, 0)
9 (0, 0). (End)
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CROSSREFS
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Cf. A336660 (another version), A336782 (with links to list of solutions and illustrations).
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KEYWORD
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nonn,hard,more
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AUTHOR
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EXTENSIONS
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a(8)-a(9) corrected by Hugo Pfoertner, based on data from Hermann Jurksch, Aug 02 2020
a(11) from Hermann Jurksch, communicated privately to Hugo Pfoertner, Aug 05 2020
a(12)-a(13) from Hermann Jurksch, communicated privately to Rainer Rosenthal, Aug 07 2020, Aug 15 2020
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STATUS
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approved
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