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0, 1, 2, 8, 19, 54, 130, 334, 806, 1995, 4816, 11746, 28357, 68748, 165972, 401388, 969036, 2341141, 5652014, 13649228, 32952151, 79563330, 192082870, 463752730, 1119598130, 2703006111, 6525634012, 15754412038, 38034515209, 91823775384, 221682203880, 535188986904, 1292060510616, 3119311948585
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OFFSET
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0,3
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COMMENTS
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a(n) is the number of free polyominoes of width 2 and height n+1 which have no symmetry, i.e., rotations by 180 degrees, flips along the short or long axis generate a different free polyomino. The three elements t, g+ and g- of sequences by Tasi et al. represent a domino in the short cross-section where either both, only the "upper" or only the "lower" square of the domino is occupied. E.g., a(3) = 8 represents 3 5-ominoes of shape the 2x4, 3 6-ominoes of shape 2x4, and 2 7-ominoes of shape 2x4. - R. J. Mathar, Jun 17 2020
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LINKS
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FORMULA
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4*a(n) = Pell(n+3) - Pell(n+2) - 2*Pell(floor((n+4)/2)) + 1, with Pell(n) = A000129(n). - Ralf Stephan, Jun 02 2007
G.f.: x*(1-x+x^2)/((1-x)*(1-2*x-x^2)*(1-2*x^2-x^4)). - Colin Barker, Apr 08 2013
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MATHEMATICA
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Table[(LucasL[n+2, 2] -4*Fibonacci[Floor[n/2]+2, 2] +2)/8, {n, 0, 40}] (* G. C. Greubel, May 24 2021 *)
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PROG
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(Sage) [(lucas_number2(n+2, 2, -1) -4*lucas_number1(2+(n//2), 2, -1) +2)/8 for n in (0..40)] # G. C. Greubel, May 24 2021
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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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EXTENSIONS
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STATUS
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approved
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