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 A090192 Carlitz-Riordan q-Catalan numbers (recurrence version) for q = -1. 33
 1, 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, -343059613650, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,6 COMMENTS Hankel transform is (-1)^C(n+1,2). - Paul Barry, Feb 15 2008 LINKS Fung Lam and Seiichi Manyama, Table of n, a(n) for n = 0..3338 (first 1002 terms from Fung Lam) FORMULA a(n+1) = Sum_{i=0..n} q^i*a(i)*a(n-i) with q=-1 and a(0)=1. G.f.: 1+x*c(-x^2), where c(x) is the g.f. of A000108; a(n) = 0^n+C((n-1)/2)(-1)^((n-1)/2)(1-(-1)^n)/2, where C(n) = A000108(n). - Paul Barry, Feb 15 2008 G.f.: 1/(1-x/(1+x/(1-x/(1+x/(1-x/(1+x/(1-.... (continued fraction). - Paul Barry, Jan 15 2009 a(n) = 2 * a(n-1) - Sum_{k=1..n} a(k-1) * a(n-k) if n>0. - Michael Somos, Jul 23 2011 G.f.: (2*x-1+sqrt(1+4*x^2))/(2*x). - Philippe Deléham, Nov 07 2011 E.g.f.: x*hypergeom([1/2],[2,3/2],-x^2)=A(x)=x*(1-(x^2)/(Q(0)+(x^2)); Q(k)=2*(k^3)+9*(k^2)+(13-2*(x^2))*k-(x^2)+6+(x^2)*(k+1)*(k+2)*((2*k+3)^2)/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Nov 22 2011 G.f.: 2 + (G(0)-1)/(2*x) where G(k)=1 - 4*x/(1 + 1/G(k+1) ); (recursively defined continued fraction). - Sergei N. Gladkovskii, Dec 08 2012 G.f.: 2 + (G(0) -1)/x, where G(k)= 1 - x/(1 + x/G(k+1) ); (continued fraction). - Sergei N. Gladkovskii, Jul 17 2013 G.f.: 1 - 1/(2*x) + G(0)/(4*x), where G(k)= 1 + 1/(1 - 2*x^2*(2*k-1)/(2*x^2*(2*k-1) - (k+1)/G(k+1) )); (continued fraction). - Sergei N. Gladkovskii, Jul 17 2013 G.f.: 1- x/(Q(0) + 2*x^2), where Q(k)= (4*x^2 - 1)*k - 2*x^2 - 1 +  2*x^2*(k+1)*(2*k+1)/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Jul 17 2013 G.f.: 1+ x/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 D-finite with recurrence: (n+3)*a(n+2) = -4*n*a(n), a(0)=a(1)=1. For nonzero terms, a(n) ~ (-1)^((n+3)/2)/sqrt(2*Pi)*2^(n+1)/(n+1)^(3/2). - Fung Lam, Mar 17 2014 a(n) = hypergeom([-n+1,-n], [2], -1). - Peter Luschny, Sep 22 2014 G.f. A(x) satisfies A(x) = 1 / (1 - x * A(-x)). - Michael Somos, Dec 26 2016 EXAMPLE G.f. = 1 + x - x^3 + 2*x^5 - 5*x^7 + 14*x^9 - 42*x^11 + 132*x^13 - 429*x^15 + ... MAPLE A090192_list := proc(n) local j, a, w; a := array(0..n); a[0] := 1; for w from 1 to n do a[w] := a[w-1]-add(a[j]*a[w-j-1], j=1..w-1) od; convert(a, list) end: A090192_list(48); # Peter Luschny, May 19 2011 a := n -> hypergeom([-n+1, -n], [2], -1); seq(round(evalf(a(n), 69)), n=0..48); # Peter Luschny, Sep 22 2014 a:= proc(n) if n::even then 0 else (-1)^((n-1)/2)*binomial(n+1, (n+1)/2)/(2*n) fi end proc: a(0):= 1: seq(a(n), n=0..100); # Robert Israel, Sep 22 2014 MATHEMATICA CoefficientList[Series[(2 x - 1 + Sqrt[1 + 4*x^2])/(2 x), {x, 0, 50}],   x] (* G. C. Greubel, Dec 24 2016 *) Table[Hypergeometric2F1[1 - n, -n, 2, -1], {n, 0, 48}] (* Michael De Vlieger, Dec 26 2016 *) PROG (PARI) {a(n) = my(A); if( n<0, 0, n++; A = vector(n); A[1] = 1; for( k=2, n, A[k] = 2 * A[k-1] - sum( j=1, k-1, A[j] * A[k-j])); A[n])}; /* Michael Somos, Jul 23 2011 */ (Sage) def A090192_list(n) :     D = [0]*(n+2); D[1] = 1     b = True; h = 1; 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(D[1])         else :             for k in range(1, h, 1) : D[k] += D[k+1]         b = not b     return R A090192_list(49) # Peter Luschny, Jun 03 2012 (Ruby) def A(q, n)   ary = [1]   (1..n).each{|i| ary << (0..i - 1).inject(0){|s, j| s + q ** j * ary[j] * ary[i - 1 - j]}}   ary end def A090192(n)   A(-1, n) end # Seiichi Manyama, Dec 24 2016 (PARI) Vec((2*x - 1 + sqrt(1+4*x^2))/(2*x) + O(x^50)) \\ G. C. Greubel, Dec 24 2016 CROSSREFS Cf. A227543. Cf. A015108 (q=-11), A015107 (q=-10), A015106 (q=-9), A015105 (q=-8), A015103 (q=-7), A015102 (q=-6), A015100 (q=-5), A015099 (q=-4), A015098 (q=-3), A015097 (q=-2), this sequence (q=-1), A000108 (q=1), A015083 (q=2), A015084 (q=3), A015085 (q=4), A015086 (q=5), A015089 (q=6), A015091 (q=7), A015092 (q=8), A015093 (q=9), A015095 (q=10), A015096 (q=11). Column k=1 of A290789. Sequence in context: A105523 A210628 A126120 * A097331 A260330 A094032 Adjacent sequences:  A090189 A090190 A090191 * A090193 A090194 A090195 KEYWORD sign AUTHOR Philippe Deléham, Jan 22 2004 STATUS approved

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Last modified October 26 09:03 EDT 2020. Contains 338027 sequences. (Running on oeis4.)