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%I #23 Jan 30 2022 15:57:47
%S 3,0,1,7,3,3,8,5,3,5,9,7,9,7,2,4,5,7,9,4,8,1,6,2,1,5,9,3,9,3,9,9,1,1,
%T 9,2,6,2,3,0,0,9,4,3,1,5,1,7,1,5,7,7,2,0,3,9,5,7,9,1,9,2,3,3,1,8,3,7,
%U 9,8,2,5,8,9,2,0,3,4,3,3,5,2,7,5,8,5,9,4,9,2,9,7,8,7,5,8,1,6,9,6,8,3,5,5,7
%N Decimal expansion of Sum_{k>=1} 1/(5^k - 1).
%H G. C. Greubel, <a href="/A248722/b248722.txt">Table of n, a(n) for n = 0..10000</a>
%F Equals Sum_{k>=1} d(k)/5^k, where d(k) is the number of divisors of k (A000005). - _Amiram Eldar_, Jun 22 2020
%e 0.301733853597972457948162159393991192623009431517157720395791923318379825892...
%p evalf( add( (1/5)^(n^2)*(1 + 2/(5^n - 1)), n = 1..12), 105); # _Peter Bala_, Jan 30 2022
%t x = 1/5; RealDigits[ Sum[ DivisorSigma[0, k] x^k, {k, 1000}], 10, 105][[1]] (* after an observation and the formula of _Amarnath Murthy_, see A073668 *)
%o (PARI) sumpos(k=1,1/(5^k-1)) \\ _M. F. Hasler_, Oct 15 2014
%Y Cf. A000005, A065442, A073668, A214369, A248721, A248723, A248724, A248725, A248726.
%K nonn,cons
%O 0,1
%A _Robert G. Wilson v_, Oct 12 2014
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