A004117 Numerators of expansion of (1-x)^(-1/3).

1, 1, 2, 14, 35, 91, 728, 1976, 5434, 135850, 380380, 1071980, 9111830, 25933670, 74096200, 637227320, 1832028545, 5280552865, 137294374490, 397431084050, 1152550143745, 10043651252635, 29217894553120, 85112997176480

Offset

0,3

Comments

For n >= 1, a(n) is also the numerator of beta(n+1/3,2/3)*sqrt(27)/(2*Pi). - Groux Roland, May 17 2011

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Formula

(1/n!) * 3^A054861(n) * Product_{k=0..n-1} (3k+1). - Ralf Stephan, Mar 13 2004

Numerators in (1-3t)^(-1/3) = 1 + t + 2*t^2 + (14/3)*t^3 + (35/3)*t^4 + (91/3)*t^5 + (728/9)*t^6 + (1976/9)*t^7 + (5434/9)*t^8 + ... = 1 + t + 4*t^2/2! + 28*t^3/3! + 280*t^4/4! + 3640*t^5/5! + 58240*t^6/6! + ... = e.g.f. for triple factorials A007559 (cf. A094638). - Tom Copeland, Dec 04 2013

Mathematica

Table[Numerator[Binomial[-1/3, n] (-1)^n], {n, 0, 40}] (* Vincenzo Librandi, Jun 13 2012 *)

Prog

(PARI) a(n)=prod(k=1, n, 3*k-2)/n!*3^sum(k=1, n, valuation(k, 3))

Crossrefs

Cf. A004128.

Cf. A004987, A007559, A047657, A054861, A034689, A053101, A072888.

Sequence in context: A367646 A367578 A134647 * A330672 A135706 A091520

Adjacent sequences: A004114 A004115 A004116 * A004118 A004119 A004120

Keyword

nonn

Author

N. J. A. Sloane

Extensions

Typo in formula fixed by Pontus von Brömssen, Nov 25 2008

Status

approved