A027875 a(n) = Product_{i=1..n} (7^i - 1).

1, 6, 288, 98496, 236390400, 3972777062400, 467389275837235200, 384914699001548351078400, 2218956256804125934296760320000, 89542886518308517126993353029713920000

Offset

0,2

Links

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

Formula

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

a(n) ~ c * 7^(n*(n+1)/2), where c = Product_{k>=1} (1-1/7^k) = A132035 = 0.836795407089037871026729798146136241352436435876... . - Vaclav Kotesovec, Nov 21 2015

a(n) = 7^(binomial(n+1,2))*(1/7;1/7)_{n}, where (a;q)_{n} is the q-Pochhammer symbol. - G. C. Greubel, Dec 24 2015

a(n) = Product_{i=1..n} A024075(i). - Michel Marcus, Dec 27 2015

G.f.: Sum_{n>=0} 7^(n*(n+1)/2)*x^n / Product_{k=0..n} (1 + 7^k*x). - Ilya Gutkovskiy, May 22 2017

Sum_{n>=0} (-1)^n/a(n) = A132035. - Amiram Eldar, May 07 2023

Mathematica

Abs@QPochhammer[7, 7, Range[0, 10]] (* Vladimir Reshetnikov, Nov 20 2015 *)
Table[Product[7^k-1, {k, n}], {n, 0, 10}] (* Harvey P. Dale, Jul 28 2022 *)

Prog

(PARI) a(n) = prod(i=1, n, 7^i-1); \\ Michel Marcus, Nov 21 2015
(Magma) [1] cat [&*[ 7^k-1: k in [1..n] ]: n in [1..11]]; // Vincenzo Librandi, Dec 24 2015

Crossrefs

Cf. A005329 (q=2), A027871 (q=3), A027637 (q=4), A027872 (q=5), A027873 (q=6), A027876 (q=8), A027877 (q=9), A027878 (q=10), A027879 (q=11), A027880 (q=12).

Cf. A132035.

Sequence in context: A203051 A128792 A340540 * A203422 A042119 A196980

Adjacent sequences: A027872 A027873 A027874 * A027876 A027877 A027878

Keyword

nonn

Author

N. J. A. Sloane

Status

approved