login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A248724 Decimal expansion of Sum_{k>=1} 1/(7^k - 1). 7
1, 9, 0, 9, 1, 0, 0, 6, 2, 4, 1, 0, 2, 6, 1, 5, 7, 8, 2, 0, 2, 1, 9, 9, 6, 4, 4, 4, 1, 7, 6, 9, 1, 1, 6, 8, 7, 6, 9, 2, 6, 8, 4, 7, 6, 0, 0, 8, 2, 6, 6, 4, 0, 8, 3, 3, 4, 7, 7, 1, 1, 0, 8, 6, 4, 0, 9, 9, 9, 6, 7, 5, 5, 8, 4, 6, 3, 0, 1, 4, 4, 0, 3, 8, 0, 0, 9, 1, 1, 6, 1, 6, 5, 9, 7, 0, 9, 1, 1, 9, 3, 4, 5, 6, 1 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..10000

FORMULA

Equals Sum_{k>=1} d(k)/7^k, where d(k) is the number of divisors of k (A000005). - Amiram Eldar, Jun 22 2020

EXAMPLE

0.1909100624102615782021996444176911687692684760082664083347711086409996755846...

MAPLE

evalf(sum(1/(7^k-1), k=1..infinity), 120) # Vaclav Kotesovec, Oct 18 2014

MATHEMATICA

x = 1/7; RealDigits[ Sum[ DivisorSigma[0, k] x^k, {k, 1000}], 10, 105][[1]] (* after an observation and the formula of Amarnath Murthy, see A073668 *)

PROG

(PARI) suminf(k=1, 1/(7^k-1)) \\ Michel Marcus, Oct 18 2014

CROSSREFS

Cf. A000005, A065442, A073668, A214369, A248721, A248722, A248723, A248725, A248726.

Sequence in context: A059058 A021015 A010680 * A278144 A198220 A131566

Adjacent sequences:  A248721 A248722 A248723 * A248725 A248726 A248727

KEYWORD

nonn,cons

AUTHOR

Robert G. Wilson v, Oct 12 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 18 15:54 EDT 2021. Contains 343089 sequences. (Running on oeis4.)