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A375817
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In an n X n grid draw straight walls between cells, starting at a border, such that the resulting figure is connected and has only one-cell wide paths; a(n) is the number of solutions not reduced for symmetries.
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2
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1, 4, 56, 1112, 25000, 607712, 15918280, 451371888, 13908978792, 466254401360, 16972978214456, 668532916285104, 28362769354991656, 1290007395847848160, 62619708755213093360, 3230982278203826268640, 176553522584025285715304, 10184062836771923067636528
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OFFSET
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1,2
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COMMENTS
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This sequence contains some, but not all of the spanning trees in A007341, a(n)<A007341(n), for n>2.
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LINKS
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EXAMPLE
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a(3) = 56. The A375770(3) = 10 distinct solutions with their multiplicities are:
._._._. ._._._. ._._._. ._._._. ._._._.
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(4) (8) (4) (2) (8)
._._._. ._._._. ._._._. ._._._. ._._._.
| | ._| | | | | ._| |_. ._| |_. | |
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(8) (8) (8) (4) (2)
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PROG
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(PARI) \\ See PARI link in A375770 for program code.
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CROSSREFS
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KEYWORD
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nonn,new
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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