

A176730


Denominators of coefficients of a series, called f, related to Airy functions.


5



1, 6, 180, 12960, 1710720, 359251200, 109930867200, 46170964224000, 25486372251648000, 17891433320656896000, 15565546988971499520000, 16437217620353903493120000, 20710894201645918401331200000, 30693545206839251070772838400000, 52854284846177190343870827724800000
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OFFSET

0,2


COMMENTS

The numerators are always 1.
Let f(z) = Sum_{n>=0} (1/a(n))*z^(3*n) and g(z) = Sum_{n>=0}(1/b(n))*z^(3*n+1) with b(n) = A176731(n) build the two independent Airy functions Ai(z) = c[1]*f(z)  c[2]*g(z) and Bi(z) = sqrt(3)*(c[1]*f(z) + c[2]*g(z)) with c[1] = 1/(3^(2/3)*Gamma(2/3)), approximately 0.35502805388781723926 and c[2] = 1/(3^(1/3)*Gamma(1/3)), approximately 0.25881940379280679840.
If y = Sum_{n >= 0} x^(3*n)/a(n), then y'' = x*y.  Michael Somos, Jul 12 2019
Define W(z) = 1 + Sum_{n >= 0} (1)^(n+1)* z^(3*n+1)/(a(n)*(3*n+1)). Then W(z) satisfies the o.d.e. W'''(z) + z*W'(z) = 0 with W(0) = 1, W'(0) = 1, and W''(0) = 0. The function 1/W(z) is the e.g.f. of A117226, which is the number of permutations of [n] avoiding the consecutive pattern 1243. In other words, Sum_{n >= 0} A117226(n)*z^n/n! = 1/W(z). See Theorem 4.3 (Case 1243 with u = 0) in Elizalde and Noy (2003).  Petros Hadjicostas, Nov 01 2019


LINKS

G. C. Greubel, Table of n, a(n) for n = 0..200
M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972, 10.4.2  5. [alternative scanned copy].
Sergi Elizalde and Marc Noy, Consecutive patterns in permutations, Adv. Appl. Math. 30 (2003), 110125; see p. 120.
Wolfdieter Lang, The first 20 terms of the f(z) and g(z) functions.
NIST's Digital Library of Mathematical Functions, Airy and Related Functions (Maclaurin Series) by Frank W. J. Olver.


FORMULA

a(n) = denominator((3^n)*risefac(1/3,n)/(3*n)!) with the rising factorials risefac(k,n) = Product_{j=0..n1} (k+j) and risefac(k,0)=1.


EXAMPLE

Rational fcoefficients: 1, 1/6, 1/180, 1/12960, 1/1710720, 1/359251200, 1/109930867200, 1/46170964224000, ....


MATHEMATICA

a[ n_] := If[ n < 0, 0, 1 / (3^(2/3) Gamma[2/3] SeriesCoefficient[ AiryAi[x], {x, 0, 3 n}])]; (* Michael Somos, Oct 14 2011 *)
a[ n_] := If[ n < 0, 0, (3*n)! / Product[ k, {k, 1, 3 n  2, 3}]]; (* Michael Somos, Oct 14 2011 *)


PROG

(PARI) {a(n) = if( n<0, 0, (3*n)! / prod( k=0, n1, 3*k + 1))}; /* Michael Somos, Oct 14 2011 */


CROSSREFS

Cf. A117226, A176731.
Column k=3 of A329070.
Sequence in context: A135395 A337756 A141121 * A225776 A051357 A251671
Adjacent sequences: A176727 A176728 A176729 * A176731 A176732 A176733


KEYWORD

nonn,frac,easy


AUTHOR

Wolfdieter Lang, Jul 14 2010


STATUS

approved



