A027871 a(n) = Product_{i=1..n} (3^i - 1).

1, 2, 16, 416, 33280, 8053760, 5863137280, 12816818094080, 84078326697164800, 1654829626053597593600, 97714379759212830706892800, 17309711516825516108403231948800

Offset

0,2

Comments

2*(10)^m|a(n) where 4*m <= n <= 4*m+3 for m >= 1. - G. C. Greubel, Nov 20 2015

Given probability p = 1/3^n that an outcome will occur at the n-th stage of an infinite process, then starting at n=1, 1-a(n)/A047656(n+1) is the probability that the outcome has occurred at or before the n-th iteration. The limiting ratio is 1-A100220 ~ 0.4398739. - Bob Selcoe, Mar 01 2016

Links

G. C. Greubel, Table of n, a(n) for n = 0..50

Formula

a(n) ~ c * 3^(n*(n+1)/2), where c = A100220 = Product_{k>=1} (1-1/3^k) = 0.560126077927948944969792243314140014379736333798... . - Vaclav Kotesovec, Nov 21 2015

a(n) = 3^(binomial(n+1,2))*(1/3;1/3)_{n}, where (a;q)_{n} is the q-Pochhammer symbol. - G. C. Greubel, Dec 24 2015

a(n) = Product_{i=1..n} A024023(i). - Michel Marcus, Dec 27 2015

G.f.: Sum_{n>=0} 3^(n*(n+1)/2)*x^n / Product_{k=0..n} (1 + 3^k*x). - Ilya Gutkovskiy, May 22 2017

From Amiram Eldar, Feb 19 2022: (Start)

Sum_{n>=0} 1/a(n) = A132324.

Sum_{n>=0} (-1)^n/a(n) = A100220. (End)

Maple

A027871 := proc(n)
    mul( 3^i-1, i=1..n) ;
end proc:
seq(A027871(n), n=0..8) ; # R. J. Mathar, Jul 13 2017

Mathematica

Table[Product[(3^k-1), {k, 1, n}], {n, 0, 20}] (* Vaclav Kotesovec, Jul 17 2015 *)
Abs@QPochhammer[3, 3, Range[0, 10]] (* Vladimir Reshetnikov, Nov 20 2015 *)

Prog

(PARI) a(n) = prod(i=1, n, 3^i-1); \\ Michel Marcus, Nov 21 2015
(Magma) [1] cat [&*[ 3^k-1: k in [1..n] ]: n in [1..11]]; // Vincenzo Librandi, Dec 24 2015

Crossrefs

Cf. A005329 (q=2), A027637 (q=4), A027872 (q=5), A027873 (q=6), A027875 (q=7), A027876 (q=8), A027877 (q=9), A027878 (q=10), A027879 (q=11), A027880 (q=12).

Cf. A047656, A100220, A132324.

Sequence in context: A181213 A283851 A130276 * A283408 A343428 A282309

Adjacent sequences: A027868 A027869 A027870 * A027872 A027873 A027874

Keyword

nonn

Author

N. J. A. Sloane

Status

approved