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A001354
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Coordination sequence for hyperbolic tesselation 3^7 (from triangle group (2,3,7)).
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2
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1, 7, 21, 56, 147, 385, 1008, 2639, 6909, 18088, 47355, 123977, 324576, 849751, 2224677, 5824280, 15248163, 39920209, 104512464, 273617183, 716339085, 1875400072, 4909861131, 12854183321
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OFFSET
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0,2
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..1000
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FORMULA
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a(n+1)=3*a(n)-a(n-1).
G.f.: (1+4*x+x^2)/(1-3*x+x^2). [Colin Barker, Apr 14 2012]
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MATHEMATICA
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CoefficientList[Series[(1+4*x+x^2)/(1-3*x+x^2), {x, 0, 30}], x] (* Vincenzo Librandi, Apr 15 2012 *)
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CROSSREFS
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7 times alternate Fibonacci numbers A001906.
Sequence in context: A146408 A050894 A146464 * A200930 A088656 A146139
Adjacent sequences: A001351 A001352 A001353 * A001355 A001356 A001357
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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