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%I #15 Feb 01 2022 01:14:40
%S 1,2,6,18,55,173,560,1858,6291,21657,75581,266797,950911,3417339,
%T 12369284,45052514,165002459,607283489,2244901889,8331383609,
%U 31030387439,115948830659,434542177289,1632963760973,6151850548775,23229299473603,87900903988155
%N a(n) = Catalan(n) + Catalan(n+1) - 1.
%H T. D. Noe, <a href="/A000778/b000778.txt">Table of n, a(n) for n = 0..200</a>
%H J. R. Stembridge, <a href="http://dx.doi.org/10.1090/S0002-9947-97-01805-9">Some combinatorial aspects of reduced words in finite Coxeter groups</a>, Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332.
%F 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
%t Table[CatalanNumber[n] + CatalanNumber[n + 1] - 1, {n, 0, 200}] (* _T. D. Noe_, Jun 20 2012 *)
%Y Cf. A000108.
%Y Equals A005807(n) - 1. Cf. A071716.
%K nonn
%O 0,2
%A _N. J. A. Sloane_
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