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 A000778 a(n) = Catalan(n) + Catalan(n+1) - 1. 2
 1, 2, 6, 18, 55, 173, 560, 1858, 6291, 21657, 75581, 266797, 950911, 3417339, 12369284, 45052514, 165002459, 607283489, 2244901889, 8331383609, 31030387439, 115948830659, 434542177289, 1632963760973, 6151850548775, 23229299473603, 87900903988155 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS T. D. Noe, Table of n, a(n) for n = 0..200 J. R. Stembridge, Some combinatorial aspects of reduced words in finite Coxeter groups, Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332. FORMULA D-finite with recurrence (n+2)*a(n) +(-5*n-4)*a(n-1) +(3*n+4)*a(n-2) +(5*n-16)*a(n-3) +2*(-2*n+7)*a(n-4)=0. - R. J. Mathar, Jun 17 2020 MATHEMATICA Table[CatalanNumber[n] + CatalanNumber[n + 1] - 1, {n, 0, 200}] (* T. D. Noe, Jun 20 2012 *) CROSSREFS Cf. A000108. Equals A005807(n) - 1. Cf. A071716. Sequence in context: A004529 A238236 A294159 * A006725 A066158 A148456 Adjacent sequences:  A000775 A000776 A000777 * A000779 A000780 A000781 KEYWORD nonn AUTHOR STATUS approved

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Last modified July 3 15:54 EDT 2022. Contains 355055 sequences. (Running on oeis4.)