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 A238438 Expansion of 1/G(0) where G(k) = 1 - q/(1 - q - q^3 / G(k+1) ). 1
 1, 1, 2, 4, 9, 21, 50, 121, 297, 738, 1853, 4694, 11982, 30790, 79586, 206786, 539784, 1414905, 3722776, 9828501, 26028969, 69129150, 184076913, 491340306, 1314412198, 3523519135, 9463563168, 25462981484, 68626114915, 185246103584, 500779373140, 1355636896041, 3674558399538, 9972405246294, 27095580261125 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS What does this sequence count? LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 FORMULA From Vaclav Kotesovec, Mar 01 2014: (Start) G.f.: 2*(1-x)/(1 - 2*x + x^3 + sqrt(1 - 4*x + 4*x^2 - 2*x^3 + x^6)). D-finite with Recurrence: (n+3)*a(n) = 2*(2*n+3)*a(n-1) - 4*n*a(n-2) + (2*n-3)*a(n-3) - (n-6)*a(n-6). a(n) ~ (6*r^2+14*r+17) * sqrt(7*r-2) / (2 * sqrt(Pi) * n^(3/2) * r^(n-1/2)), where r = 1/3*(-2 - 2*(2/(47 + 3*sqrt(249)))^(1/3) + (1/2*(47 + 3*sqrt(249)))^(1/3)) = 0.3532099641993244294831... is the root of the equation r^3 + 2*r^2 + 2*r = 1. (End) G.f. A(q) satisfies 0 = -q^3*A(q)^2 + (q^3 - 2*q + 1)*A(q) + (q - 1). MATHEMATICA CoefficientList[Series[2*(1-x)/(1 - 2*x + x^3 + Sqrt[1 - 4*x + 4*x^2 - 2*x^3 + x^6]), {x, 0, 20}], x] (* Vaclav Kotesovec, Mar 01 2014 *) PROG (PARI) N = 66;  q = 'q + O('q^N); G(k) = if(k>N, 1,  1 - q/(1 - q - q^3 / G(k+1) ) ); Vec( 1/G(0) ) CROSSREFS Cf. A086581: 1/G(0) where G(k) = 1 - q/(1 - q - q^2 / G(k+1) ). Cf. A119370: 1/G(0) where G(k) = 1 - q/(1 - (q + q^2) / G(k+1) ). Sequence in context: A261664 A091964 A092423 * A257104 A318008 A199410 Adjacent sequences:  A238435 A238436 A238437 * A238439 A238440 A238441 KEYWORD nonn AUTHOR Joerg Arndt, Feb 27 2014 STATUS approved

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Last modified October 30 06:31 EDT 2020. Contains 338077 sequences. (Running on oeis4.)