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Search: id:A060521
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| A060521 |
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Number of 3 X n grids of black and white cells, no 3 of same color vertically or horizontally contiguous. |
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+0
1
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| 6, 36, 102, 378, 1260, 4374, 14946, 51384, 176238, 605022, 2076288, 7126302, 24457806, 83942100, 288096942, 988778082, 3393583068, 11647114446, 39974047290, 137194888728, 470866430838, 1616060190870, 5546478488640
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The conjectured recursion is correct: For each n count the solutions separately where the last two rows differ in 0, 1, 2, or 3 places; a linear recursion is then readily found. The corresponding matrix has characteristic polynomial x^4 - 2 x^3 - 5 x^2 + 1, matching the recursion recursion a(n+4) = 2a(n+3) + 5a(n+2) - a(n). [From Hagen von Eitzen (math(AT)von-eitzen.de), Oct 21 2009]
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FORMULA
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Almost surely satisfies a(n+4) = 2a(n+3) + 5a(n+2) - a(n).
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CROSSREFS
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Sequence in context: A080857 A108158 A086113 this_sequence A036141 A061804 A083374
Adjacent sequences: A060518 A060519 A060520 this_sequence A060522 A060523 A060524
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KEYWORD
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nonn
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AUTHOR
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Tom Womack (tom(AT)womack.net)
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EXTENSIONS
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More terms from Hagen von Eitzen (math(AT)von-eitzen.de), Oct 21 2009
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