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A232230
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Expansion of (1 - 2*x + x^2 + x^3 + x^5) / ((1 - x)*(1 - 2*x - x^3)).
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1
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1, 1, 2, 6, 14, 32, 72, 160, 354, 782, 1726, 3808, 8400, 18528, 40866, 90134, 198798, 438464, 967064, 2132928, 4704322, 10375710, 22884350, 50473024, 111321760, 245527872, 541528770, 1194379302, 2634286478, 5810101728, 12814582760, 28263452000, 62337005730, 137488594222, 303240640446
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OFFSET
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0,3
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LINKS
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A. Goupil, M.-E. Pellerin and J. de Wouters d'Oplinter, Snake Polyominoes, arXiv preprint arXiv:1307.8432 [math.CO], 2013-2014.
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FORMULA
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a(n) = 3*a(n-1) - 2*a(n-2) + a(n-3) - a(n-4) for n>3. - Colin Barker, Dec 05 2018
a(n) = 2*a(n-1) + a(n-3) + 2 for n>4. - Greg Dresden, Feb 09 2020
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MATHEMATICA
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Join[{1, 1}, LinearRecurrence[{3, -2, 1, -1}, {2, 6, 14, 32}, 33]] (* Jean-François Alcover, Dec 05 2018 *)
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PROG
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(PARI) Vec((1 - 2*x + x^2 + x^3 + x^5) / ((1 - x)*(1 - 2*x - x^3)) + O(x^40)) \\ Colin Barker, Dec 05 2018
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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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