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A094556
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Number of walks of length n between opposite vertices on a triangular prism.
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2
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0, 1, 0, 7, 8, 51, 100, 407, 1008, 3451, 9500, 30207, 87208, 268451, 791700, 2402407, 7152608, 21567051, 64482700, 193885007, 580781208, 1744091251, 5228778500, 15693326007, 47065997008, 141225953051, 423621935100, 1270977653407
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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FORMULA
| G.f.: x(1-2x+2x^2)/((1-x)(1+2x)(1-3x)); a(n)=3^n/6-(-2)^n/3-1/6+0^n/3; a(n)=2a(n-1)+5a(n-2)-6a(n-3).
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MATHEMATICA
| LinearRecurrence[{2, 5, -6}, {0, 1, 0, 7}, 30] (* or *) CoefficientList[ Series[ x (1-2x+2x^2)/((1-x)(1+2x)(1-3x)), {x, 0, 30}], x] (* From Harvey P. Dale, Jul 13 2011 *)
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CROSSREFS
| Cf. A094554, A094555.
Sequence in context: A116554 A038274 A201919 * A041023 A041108 A137145
Adjacent sequences: A094553 A094554 A094555 * A094557 A094558 A094559
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), May 11 2004
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