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 A007854 G.f.: 1/(1 - 3*x*C(x)), where C(x) = (1 - sqrt(1 - 4*x))/(2*x) = g.f. for the Catalan numbers A000108. 17
 1, 3, 12, 51, 222, 978, 4338, 19323, 86310, 386250, 1730832, 7763550, 34847796, 156503064, 703149438, 3160160811, 14206181382, 63874779714, 287242041528, 1291872728826, 5810776384932, 26138647551564, 117587214581508 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Chains in rooted plane trees on n nodes. The Hankel transform of the aerated sequence with g.f. 1/(1-3x^2c(x^2)) is also 3^n. In general, the expansions of 1/(1-k*x*c(x)) and 1/(1-k*x^2*c(x^2)) have Hankel transform k^n. - Paul Barry, Jan 20 2007 Binomial transform of A112657. - Philippe Deléham, Nov 25 2007 Row sums of the Riordan matrix (1/sqrt(1-4x),(1-sqrt(1-4x))/(2*sqrt(1-4x))) (A116395) [Emanuele Munarini, Apr 26 2011] Numbers have the same parity as the Catalan numbers, that is, a(n) is even except for n of the form 2^m - 1. Follows from C(x) = 1/(1 - x*C(x)) = 1/(1 - 3*x*C(x)) (mod 2). - Peter Bala, Jul 24 2016 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 M. Klazar, Twelve countings with rooted plane trees, European Journal of Combinatorics 18 (1997), 195-210; Addendum, 18 (1997), 739-740. J.-C. Novelli and J.-Y. Thibon, Free quasi-symmetric functions of arbitrary level, arXiv:math/0405597 [math.CO], 2004. FORMULA a(n) = (9*a(n-1)-3*A000108(n-2))/2 = 3*A049027(n-1) = A067336(n-1)*3/2 = A049027(n-1)+A067336(n-1) = A067347(3, n-1). - Henry Bottomley, Jan 16 2002 a(n) = Sum_{k>=0} A106566(n, k)*3^k. - Philippe Deléham, Aug 11 2005 The Hankel transform of this sequence is A000244 = [1, 3, 9, 27, 81, 243, 729, ...](powers of 3). - Philippe Deléham, Nov 26 2006 a(n) = Sum_{k = 0..n} C(2n,n-k)(2k+1)2^k/(n+k+1). - Paul Barry, Jan 20 2007 a(n) = Sum_{k = 0..n} A039599(n,k)*2^k. - Philippe Deléham, Sep 08 2007 a(n) = Sum_{k = 0..n} A116395(n,k). - Vladimir Kruchinin, Mar 09 2011 From Emanuele Munarini, Apr 26 2011 (Start) a(n) = Sum_{k = 1..n} C(2*n-k,n-k)*(k*3^k)/(2*n-k), for n>0. a(n) = (1/4)*(9/2)^n-3*Sum_{k=0..n} C(2*k,k)/(2k-1)*(9/2)^(n-k). Recurrence: 2*(n+2)*a(n+2)-(17*n+22)*a(n+1)+18*(2*n+1)*a(n)=0. (End) a(n) = upper left term in M^n, M = the infinite square production matrix: 3, 3, 0, 0, 0, 0,... 1, 1, 1, 0, 0, 0,... 1, 1, 1, 1, 0, 0,... 1, 1, 1, 1, 1, 0,... 1, 1, 1, 1, 1, 1,... ... - Gary W. Adamson, Jul 14 2011 MATHEMATICA CoefficientList[Series[(1+3Sqrt[1-4x])/(4-18x), {x, 0, 25}], x]) (* Emanuele Munarini, Apr 26 2011 *) PROG (Maxima) makelist(kron_delta(n, 0)+sum(binomial(2*n-k, n-k)*(k*3^k)/(2*n-k), k, 1, n), n, 0, 12); \\ Emanuele Munarini, Apr 26 2011 CROSSREFS Cf. A000108, A000984, A076035, A076036, A067347, A116395, A126694. Sequence in context: A104268 A081704 A166482 * A151182 A151316 A151183 Adjacent sequences:  A007851 A007852 A007853 * A007855 A007856 A007857 KEYWORD nonn,easy AUTHOR Martin Klazar (klazar(AT)kam.mff.cuni.cz) EXTENSIONS More terms from Henry Bottomley, Jan 16 2002 STATUS approved

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Last modified October 19 22:28 EDT 2018. Contains 316378 sequences. (Running on oeis4.)