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 A000180 Expansion of E.g.f. exp(-x)/(1-3x). (Formerly M2063 N0816) 7
 1, 2, 13, 116, 1393, 20894, 376093, 7897952, 189550849, 5117872922, 153536187661, 5066694192812, 182400990941233, 7113638646708086, 298772823161739613, 13444777042278282584, 645349298029357564033, 32912814199497235765682 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 REFERENCES 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). LINKS T. D. Noe, Table of n, a(n) for n=0..100 FORMULA 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(n+1) = (3*n+2)*a(n) + 3*n*a(n-1). - 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 a(n) = 3*n*a(n-1)+(-1)^n for n > 0. - Werner Schulte, Mar 09 2020 MATHEMATICA 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 *) PROG (PARI) x='x+O('x^33); Vec(serlaplace(exp(-x) / (1-3*x))) \\ Gheorghe Coserea, Aug 06 2015 CROSSREFS Column k=3 of A320032. Sequence in context: A208958 A209052 A209217 * A215715 A292437 A317196 Adjacent sequences: A000177 A000178 A000179 * A000181 A000182 A000183 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Simon Plouffe EXTENSIONS More terms from Benoit Cloitre, Nov 02 2003 STATUS approved

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Last modified September 22 07:13 EDT 2023. Contains 365519 sequences. (Running on oeis4.)