0,2

Given probability p = 1/5^n that an outcome will occur at the n-th stage of an infinite process, then starting at n=1, 1 - a(n)/A109345(n+1) is the probability that the outcome has occurred at or before the n-th iteration. The limiting ratio is 1-A100222 ~ 0.2396672. - Bob Selcoe, Mar 01 2016

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

4^n|a(n) for n >= 1. - G. C. Greubel, Nov 21 2015

a(n) ~ c * 5^(n*(n+1)/2), where c = Product_{k>=1} (1-1/5^k) = A100222 . - Vaclav Kotesovec, Nov 21 2015

a(n) = 5^(binomial(n+1,2))*(1/5; 1/5)_{n}, where (a;q)_{n} is the q-Pochhammer symbol. - G. C. Greubel, Dec 23 2015

a(n) = Product_{i=1..n} A024049(i). - Michel Marcus, Dec 27 2015

G.f.: Sum_{n>=0} 5^(n*(n+1)/2)*x^n / Product_{k=0..n} (1 + 5^k*x). - Ilya Gutkovskiy, May 22 2017

Sum_{n>=0} (-1)^n/a(n) = A100222. - Amiram Eldar, May 07 2023

A027872 := proc(n)

mul( 5^i-1, i=1..n) ;

end proc: # R. J. Mathar, Mar 12 2013

Table[Product[(5^k-1), {k, 1, n}], {n, 0, 20}] (* Vaclav Kotesovec, Jul 17 2015 *)

Abs@QPochhammer[5, 5, Range[0, 10]] (* Vladimir Reshetnikov, Nov 20 2015 *)

Join[{1}, FoldList[Times, 5^Range[10]-1]] (* Harvey P. Dale, Dec 28 2021 *)

(PARI) a(n) = prod(i=1, n, 5^i-1); \\ Michel Marcus, Nov 21 2015

(Magma) [1] cat [&*[ 5^k-1: k in [1..n] ]: n in [1..11]]; // Vincenzo Librandi, Dec 24 2015

Cf. A005329 (q=2), A027871 (q=3), A027637 (q=4), A027873 (q=6), A027875 (q=7), A027876 (q=8), A027877 (q=9), A027878 (q=10), A027879 (q=11), A027880 (q=12).

Cf. A109345, A100222.

Sequence in context: A065140 A007106 A111637 * A308146 A203517 A146514

Adjacent sequences: A027869 A027870 A027871 * A027873 A027874 A027875

approved