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A123854 Denominators in an asymptotic expansion for the cubic recurrence sequence A123851. 15
1, 4, 32, 128, 2048, 8192, 65536, 262144, 8388608, 33554432, 268435456, 1073741824, 17179869184, 68719476736, 549755813888, 2199023255552, 140737488355328, 562949953421312, 4503599627370496, 18014398509481984, 288230376151711744, 1152921504606846976 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

A cubic analog of the asymptotic expansion A116603 of Somos's quadratic recurrence sequence A052129. Numerators are A123853.

Equals 2^A004134(n); also the denominators in expansion of (1-x)^(-1/4). - Alexander Adamchuk, Oct 27 2006

All terms are powers of 2 and log_2 a(n) = A004134(n) = 3*n - A000120(n). - Alexander Adamchuk, Oct 27 2006 [Edited by Petros Hadjicostas, May 14 2020]

Is this the same sequence as A088802? - N. J. A. Sloane, Mar 21 2007

Almost certainly this is the same as A088802. - Michael Somos, Aug 23 2007

Denominators of Gegenbauer_C(2n,1/4,2). The denominators of Gegenbauer_C(n,1/4,2) give the doubled sequence. - Paul Barry, Apr 21 2009

REFERENCES

S. R. Finch, Mathematical Constants, Cambridge University Press, Cambridge, 2003, p. 446.

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

T. M. Apostol, On the Lerch zeta function, Pacific J. Math. 1 (1951), 161-167. [In Eq. (3.7), p. 166, the index in the summation for the Apostol-Bernoulli numbers should start at s = 0, not at s = 1. - Petros Hadjicostas, Aug 09 2019]

Jonathan Sondow and Petros Hadjicostas, The generalized-Euler-constant function gamma(z) and a generalization of Somos's quadratic recurrence constant, arXiv:math/0610499 [math.CA], 2006.

Jonathan Sondow and Petros Hadjicostas, The generalized-Euler-constant function gamma(z) and a generalization of Somos's quadratic recurrence constant, J. Math. Anal. Appl. 332 (2007), 292-314.

Eric Weisstein's World of Mathematics, Somos's Quadratic Recurrence Constant.

Aimin Xu, Asymptotic expansion related to the Generalized Somos Recurrence constant, International Journal of Number Theory 15(10) (2019), 2043-2055. [The author gives recurrences and other formulas for the coefficients of the asymptotic expansion using the Apostol-Bernoulli numbers (see the reference above) and the Bell polynomials. - Petros Hadjicostas, Aug 09 2019]

FORMULA

From Alexander Adamchuk, Oct 27 2006: (Start)

a(n) = 2^A004134(n).

a(n) = 2^(3n - A000120(n)). (End)

a(n) = denominator(binomial(1/4,n)). - Peter Luschny, Apr 07 2016

EXAMPLE

A123851(n) ~ c^(3^n)*n^(- 1/2)/(1 + 3/(4*n) - 15/(32*n^2) + 113/(128*n^3) - 5397/(2048*n^4) + ...) where c = 1.1563626843322... is the cubic recurrence constant A123852.

MAPLE

f:=proc(t, x) exp(sum(ln(1+m*x)/t^m, m=1..infinity)); end; for j from 0 to 29 do denom(coeff(series(f(3, x), x=0, 30), x, j)); od;

# Alternatively:

A123854 := n -> denom(binomial(1/4, n)):

seq(A123854(n), n=0..25); # Peter Luschny, Apr 07 2016

MATHEMATICA

Denominator[CoefficientList[Series[ 1/Sqrt[Sqrt[1-x]], {x, 0, 25}], x]] (* Robert G. Wilson v, Mar 23 2014 *)

PROG

(Sage) # uses[A000120]

def A123854(n): return 1 << (3*n-A000120(n))

[A123854(n) for n in (0..25)]  # Peter Luschny, Dec 02 2012

(PARI) vector(25, n, n--; denominator(binomial(1/4, n)) ) \\ G. C. Greubel, Aug 08 2019

CROSSREFS

Cf. A052129, A112302, A116603, A123851, A123852, A123853 (numerators).

Cf. A004134, A004130, A000120.

Sequence in context: A239056 A088658 A088802 * A301843 A332430 A302070

Adjacent sequences:  A123851 A123852 A123853 * A123855 A123856 A123857

KEYWORD

frac,nonn

AUTHOR

Petros Hadjicostas and Jonathan Sondow, Oct 15 2006

STATUS

approved

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Last modified March 7 17:35 EST 2021. Contains 341899 sequences. (Running on oeis4.)