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 A126120 Catalan numbers (A000108) interpolated with 0's. 35
 1, 0, 1, 0, 2, 0, 5, 0, 14, 0, 42, 0, 132, 0, 429, 0, 1430, 0, 4862, 0, 16796, 0, 58786, 0, 208012, 0, 742900, 0, 2674440, 0, 9694845, 0, 35357670, 0, 129644790, 0, 477638700, 0, 1767263190, 0, 6564120420, 0, 24466267020, 0, 91482563640, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Inverse binomial transform of A001006. The Hankel transform of this sequence gives A000012 = [1,1,1,1,1,...]. Counts returning walks of length n on a 1-d integer lattice with step set {+1,-1} which stay in the chamber x >= 0. - Andrew V. Sutherland, Feb 29 2008 Moment sequence of the trace of a random matrix in G=USp(2)=SU(2). If X=tr(A) is a random variable (A distributed according to the Haar measure on G) then a(n) = E[X^n]. - Andrew V. Sutherland, Feb 29 2008 Essentially the same as A097331. - R. J. Mathar, Jun 15 2008 Number of distinct proper binary trees with n nodes. - Chris R. Sims (chris.r.sims(AT)gmail.com), Jun 30 2010 Number of n-step walks that start and end at origin with the constraint that they are never negative. - Benjamin Phillabaum, Mar 07 2011 -a(n-1), with a(-1):=0, n>=0, is the Z-sequence for the Riordan array A049310 (Chebyshev S). For the definition see that triangle. - Wolfdieter Lang, Nov 04 2011 See A180874 (also A238390 and A097610) and A263916 for relations to the general Bell A036040, cycle index A036039, and cumulant expansion polynomials A127671 through the Faber polynomials. - Tom Copeland, Jan 26 2016 Number of excursions (walks starting at the origin, ending on the x-axis, and never go below the x-axis in between) with n steps from {-1,1}. - David Nguyen, Dec 20 2016 REFERENCES Jerome Spanier and Keith B. Oldham, "Atlas of Functions", Ch. 49, Hemisphere Publishing Corp., 1987. LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 V. E. Adler, Set partitions and integrable hierarchies, arXiv:1510.02900 [nlin.SI], 2015. Martin Aigner, Catalan and other numbers: a recurrent theme, in Algebraic Combinatorics and Computer Science, a Tribute to Gian-Carlo Rota, pp.347-390, Springer, 2001. C. Banderier, C. Krattenthaler, A. Krinik, D. Kruchinin, V. Kruchinin, D. Nguyen, and M. Wallner, Explicit formulas for enumeration of lattice paths: basketball and the kernel method, arXiv:1609.06473 [math.CO], 2016. Radica Bojicic, Marko D. Petkovic and Paul Barry, Hankel transform of a sequence obtained by series reversion II-aerating transforms, arXiv:1112.1656 [math.CO], 2011. Francesc Fite, Kiran S. Kedlaya, Victor Rotger and Andrew V. Sutherland, Sato-Tate distributions and Galois endomorphism modules in genus 2, arXiv:1110.6638 [math.NT], 2011. Aoife Hennessy, A Study of Riordan Arrays with Applications to Continued Fractions, Orthogonal Polynomials and Lattice Paths, Ph. D. Thesis, Waterford Institute of Technology, Oct. 2011. Kiran S. Kedlaya and Andrew V. Sutherland, HyperellipticCurves, L-Polynomials, and Random Matrices. In: Arithmetic, Geometry, Cryptography, and Coding Theory: International Conference, November 5-9, 2007, CIRM, Marseilles, France. (Contemporary Mathematics; v.487) E. Rowland, Pattern avoidance in binary trees, J. Comb. Theory A 117 (6) (2010) 741-758, Sec. 3.1 Yidong Sun and Fei Ma, Minors of a Class of Riordan Arrays Related to Weighted Partial Motzkin Paths, arXiv:1305.2015 [math.CO], 2013. Y. Wang, Z.-H. Zhang, Combinatorics of Generalized Motzkin Numbers, J. Int. Seq. 18 (2015) # 15.2.4 FORMULA a(2*n) = A000108(n), a(2*n+1) = 0. a(n) = A053121(n,0). (1/Pi) Integral_{0 .. Pi} (2*cos(x))^n *2*sin^2(x) dx. - Andrew V. Sutherland, Feb 29 2008 G.f.: 1/(1-x^2/(1-x^2/(1-x^2/(1-x^2/(1-...(continued fraction). - Philippe Deléham, Nov 24 2009 G.f. A(x) satisfies A(x) = 1 + x^2*A(x)^2. - Vladimir Kruchinin, Feb 18 2011 E.g.f.:I_1(2x)/x Where I_n(x) is the modified Bessel function. - Benjamin Phillabaum, Mar 07 2011 Apart form the first term the e.g.f. is given by x*HyperGeom([1/2],[3/2,2], x^2). - Benjamin Phillabaum, Mar 07 2011 a(n) = Integral_{x=-2..2} x^n*sqrt((2-x)*(2+x)))/(2*Pi). - Peter Luschny, Sep 11 2011 (n+2)*a(n) + (n+1)*a(n-1) + 4*(-n+1)*a(n-2) + 4*(-n+2)*a(n-3) = 0. - R. J. Mathar, Dec 04 2012 E.g.f.: E(0)/(1-x) where E(k) = 1-x/(1-x/(x-(k+1)*(k+2)/E(k+1))); (continued fraction). - Sergei N. Gladkovskii, Apr 05 2013 G.f.: 3/2- sqrt(1-4*x^2)/2 = 1/x^2 + R(0)/x^2, where R(k) = 2*k-1 - x^2*(2*k-1)*(2*k+1)/R(k+1); (continued fraction). - Sergei N. Gladkovskii, Oct 28 2013 G.f.: 1/Q(0), where Q(k) = 2*k+1 + x^2*(1-4*(k+1)^2)/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Jan 09 2014 a(n) = n!*[x^n]hypergeom([],[2],x^2). - Peter Luschny, Jan 31 2015 a(n) = 2^n*hypergeom([3/2,-n],[3],2). - Peter Luschny, Feb 03 2015 a(n) = ((-1)^n+1)*2^(2*floor(n/2)-1)*Gamma(floor(n/2)+1/2)/(sqrt(Pi)* Gamma(floor(n/2)+2)). - Ilya Gutkovskiy, Jul 23 2016 EXAMPLE G.f. = 1 + x^2 + 2*x^4 + 5*x^6 + 14*x^8 + 42*x^10 + 132*x^12 + 429*x^14 + ... MAPLE with(combstruct): grammar := { BB = Sequence(Prod(a, BB, b)), a = Atom, b = Atom }: seq(count([BB, grammar], size=n), n=0..47); # Zerinvary Lajos, Apr 25 2007 BB := {E=Prod(Z, Z), S=Union(Epsilon, Prod(S, S, E))}: ZL:=[S, BB, unlabeled]: seq(count(ZL, size=n), n=0..45); # Zerinvary Lajos, Apr 22 2007 BB := [T, {T=Prod(Z, Z, Z, F, F), F=Sequence(B), B=Prod(F, Z, Z)}, unlabeled]: seq(count(BB, size=n+1), n=0..45); # valid for n> 0. # Zerinvary Lajos, Apr 22 2007 seq(n!*coeff(series(hypergeom([], [2], x^2), x, n+2), x, n), n=0..45); # Peter Luschny, Jan 31 2015 MATHEMATICA a[n_?EvenQ] := CatalanNumber[n/2]; a[n_] = 0; Table[a[n], {n, 0, 45}] (* Jean-François Alcover, Sep 10 2012 *) a[ n_] := If[ n < 0, 0, n! SeriesCoefficient[ BesselI[ 1, 2 x] / x, {x, 0, n}]]; (* Michael Somos, Mar 19 2014 *) PROG (Sage) def A126120_list(n) :     D = [0]*(n+2); D[1] = 1     b = True; h = 2; R = []     for i in range(2*n-1) :         if b :             for k in range(h, 0, -1) : D[k] -= D[k-1]             h += 1; R.append(abs(D[1]))         else :             for k in range(1, h, 1) : D[k] += D[k+1]         b = not b     return R A126120_list(46) # Peter Luschny, Jun 03 2012 (MAGMA) &cat [[Catalan(n), 0]: n in [0..30]]; // Vincenzo Librandi, Jul 28 2016 CROSSREFS Cf. A000108. Cf. A036039, A036040,  A097610, A127671, A180874, A238390, A263916. Sequence in context: A242839 A105523 A210628 * A090192 A097331 A260330 Adjacent sequences:  A126117 A126118 A126119 * A126121 A126122 A126123 KEYWORD nonn AUTHOR Philippe Deléham, Mar 06 2007 EXTENSIONS An erroneous comment removed by Tom Copeland, Jul 23 2016 STATUS approved

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Last modified July 18 08:22 EDT 2018. Contains 312735 sequences. (Running on oeis4.)