A248723 - OEIS

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A248723

Decimal expansion of the Sum_{k>=1} 1/(6^k - 1).

2, 3, 4, 1, 4, 9, 1, 3, 0, 1, 3, 4, 8, 0, 9, 2, 0, 6, 4, 8, 5, 1, 1, 1, 6, 7, 2, 8, 1, 3, 8, 7, 2, 9, 1, 8, 5, 4, 6, 3, 6, 1, 0, 3, 4, 7, 8, 6, 5, 1, 3, 8, 9, 8, 5, 2, 2, 4, 2, 1, 3, 8, 6, 7, 1, 0, 2, 3, 8, 1, 9, 8, 6, 6, 2, 8, 7, 9, 2, 3, 2, 2, 5, 6, 7, 8, 8, 7, 9, 5, 0, 1, 8, 7, 8, 3, 9, 1, 2, 6, 6, 5, 5, 3, 4

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OFFSET

0,1

LINKS

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

FORMULA

Equals Sum_{k>=1} d(k)/6^k, where d(k) is the number of divisors of k (A000005). - Amiram Eldar, Jun 22 2020

EXAMPLE

0.2341491301348092064851116728138729185463610347865138985224213867102381986628...

MAPLE

evalf(sum(1/(6^k-1), k=1..infinity), 120); # Vaclav Kotesovec, Oct 18 2014

# second program with faster converging series

evalf( add( (1/6)^(n^2)*(1 + 2/(6^n - 1)), n = 1..11), 105); # Peter Bala, Jan 30 2022

MATHEMATICA

x = 1/6; 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/(6^k-1)) \\ Michel Marcus, Oct 18 2014

CROSSREFS

Cf. A000005, A065442, A073668, A214369, A248721, A248722, A248724, A248725, A248726.

Sequence in context: A317088 A276380 A352724 * A117742 A117716 A211234

Adjacent sequences: A248720 A248721 A248722 * A248724 A248725 A248726

KEYWORD

nonn,cons

AUTHOR

Robert G. Wilson v, Oct 12 2014

STATUS

approved