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 A156016 Expansion of (1-x-sqrt(1-6x-3x^2))/(2x). 2
 1, 3, 9, 36, 162, 783, 3969, 20817, 112023, 615033, 3431403, 19398690, 110880900, 639730305, 3720657807, 21790419444, 128398625658, 760668489729, 4528069760691, 27070491820644, 162464919528222, 978463778897637 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Transform of Catalan numbers by Riordan array ((1+x)/(1-x), x(1+x)/(1-x)^2). LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 M. Dziemianczuk, On Directed Lattice Paths With Additional Vertical Steps, arXiv preprint arXiv:1410.5747, 2014 FORMULA a(n) = sum( k=0..n, sum( j=0..k+1, C(k+1,j)*C(n+k-j,n-k-j) )*A000108(k) ). a(n+1) = 3*A107264(n-1).  - Philippe Deléham, Feb 04 2009 Conjecture: (n+1)*a(n) +3*(-2*n+1)*a(n-1) +3*(-n+2)*a(n-2)=0. - R. J. Mathar, Dec 03 2014 MATHEMATICA CoefficientList[Series[(1-x-Sqrt[1-6x-3x^2])/(2x), {x, 0, 30}], x] (* Harvey P. Dale, Jul 27 2014 *) CROSSREFS Cf. A100239. Sequence in context: A058540 A245888 A295739 * A032314 A144352 A107895 Adjacent sequences:  A156013 A156014 A156015 * A156017 A156018 A156019 KEYWORD nonn,easy AUTHOR Paul Barry, Feb 01 2009 STATUS approved

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Last modified January 15 20:47 EST 2019. Contains 319184 sequences. (Running on oeis4.)