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A162673
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Number of different fixed (possibly) disconnected trominoes bounded (not necessarily tightly) by an n*n square
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5
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0, 4, 48, 204, 580, 1320, 2604, 4648, 7704, 12060, 18040, 26004, 36348, 49504, 65940, 86160, 110704, 140148, 175104, 216220, 264180, 319704, 383548, 456504, 539400, 633100, 738504, 856548, 988204, 1134480, 1296420, 1475104, 1671648, 1887204
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OFFSET
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1,2
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COMMENTS
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Fixed quasi-trominoes.
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LINKS
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FORMULA
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a(n)=n*(n-1)*(3*n^2-3*n-2)/2.
G.f.: 4*x^2*(1+7*x+x^2)/(1-x)^5. [Colin Barker, Apr 25 2012]
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EXAMPLE
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a(2)=4: the four rotations of the (connected) L tromino
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MATHEMATICA
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LinearRecurrence[{5, -10, 10, -5, 1}, {0, 4, 48, 204, 580}, 40] (* Harvey P. Dale, Aug 09 2017 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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