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 A126986 Expansion of 1/(1+4*x*c(x)), c(x) the g.f. of Catalan numbers A000108. 6
 1, -4, 12, -40, 124, -408, 1272, -4176, 13020, -42808, 133096, -439344, 1358872, -4514800, 13853040, -46469280, 140945820, -479312760, 1430085000, -4958382960, 14453014920, -51500944080, 145230007440, -537922074720, 1446902948184, -5662012752048, 14228883685392 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Hankel transform is (-4)^n. For n>=37, all terms are negative. - Vaclav Kotesovec, May 30 2019 LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 FORMULA a(n) = Sum_{k=0..n} A039599(n,k)*(-5)^k. G.f.: 1/(3 - 2*sqrt(1-4*x)). - G. C. Greubel, May 29 2019 a(n) ~ -4^n / (9*sqrt(Pi)*n^(3/2)). - Vaclav Kotesovec, May 30 2019 MAPLE c:=(1-sqrt(1-4*x))/2/x: ser:=series(1/(1+4*x*c), x=0, 30): seq(coeff(ser, x, n), n=0..27); # Emeric Deutsch, Mar 23 2007 MATHEMATICA CoefficientList[Series[1/(3-2*Sqrt[1-4*x]), {x, 0, 30}], x] (* G. C. Greubel, May 29 2019 *) PROG (PARI) my(x='x+O('x^30)); Vec(1/(3-2*sqrt(1-4*x))) \\ G. C. Greubel, May 29 2019 (MAGMA) R:=PowerSeriesRing(Rationals(), 30); Coefficients(R!( 1/(3 - 2*Sqrt(1-4*x)) )); // G. C. Greubel, May 29 2019 (Sage) (1/(3-2*sqrt(1-4*x))).series(x, 30).coefficients(x, sparse=False) # G. C. Greubel, May 29 2019 CROSSREFS Sequence in context: A056274 A058353 A104525 * A090576 A152174 A087206 Adjacent sequences:  A126983 A126984 A126985 * A126987 A126988 A126989 KEYWORD sign AUTHOR Philippe Deléham, Mar 21 2007 EXTENSIONS More terms from Emeric Deutsch, Mar 23 2007 STATUS approved

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Last modified October 21 06:01 EDT 2019. Contains 328291 sequences. (Running on oeis4.)