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A000180
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Expansion of E.g.f. exp(-x)/(1-3x).
(Formerly M2063 N0816)
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7
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1, 2, 13, 116, 1393, 20894, 376093, 7897952, 189550849, 5117872922, 153536187661, 5066694192812, 182400990941233, 7113638646708086, 298772823161739613, 13444777042278282584, 645349298029357564033, 32912814199497235765682
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OFFSET
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0,2
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REFERENCES
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J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 83.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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a(n) = Sum_{k=0..n} (-1)^(n+k)*binomial(n,k)*k!*3^k. - Benoit Cloitre, Nov 02 2003
a(n) = {(3^n*n!)/exp(1/3)}, where {x} = nearest integer. - Simon Plouffe, Feb 17 2011
Conjecture: (n+1)*a(n) -(n+1)*(3*n-1)*a(n-1) -3*(n-1)*(n+1)*a(n-2) = 0. - R. J. Mathar, Jul 24 2012
E.g.f.: exp(-x)/(1-3x) = A(x) satisfies (1-3x)A' - (2+3x)A = 0. - Gheorghe Coserea, Aug 06 2015
a(0) = 1; a(n) = Sum_{k=1..n} binomial(n,k) * (3*k - 1) * a(n-k). - Ilya Gutkovskiy, Jan 17 2020
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MATHEMATICA
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FunctionExpand @ Table[ Gamma[n, -1/3]*3^(n-1)/Exp[ 1/3 ], {n, 24}]
Range[0, 19]! CoefficientList[Series[Exp[-x]/(1 - 3 x), {x, 0, 19}], x] (* Vincenzo Librandi, Aug 15 2015 *)
a[n_] := 3^n n! Sum[(-1)^i/(3^i i!), {i, 0, n}]; Table[a[n], {n, 0, 20}] (* Gerry Martens , May 06 2016 *)
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PROG
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(PARI) x='x+O('x^33); Vec(serlaplace(exp(-x) / (1-3*x))) \\ Gheorghe Coserea, Aug 06 2015
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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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