This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A248725 #24 Jan 30 2022 15:57:58
%S A248725 1,6,0,9,6,6,1,8,4,3,1,5,0,6,2,3,9,6,8,0,5,3,0,2,5,6,4,1,4,3,6,4,2,8,
%T A248725 8,5,5,5,0,7,4,3,8,5,6,0,2,5,3,2,8,3,4,6,3,6,0,8,3,5,9,1,8,6,4,7,8,2,
%U A248725 3,9,4,0,8,5,8,0,0,6,3,6,9,1,7,7,9,2,3,4,5,3,1,0,0,9,3,2,5,4,0,2,5,2,9,6,4
%N A248725 Decimal expansion of Sum_{k>=1} 1/(8^k - 1).
%H A248725 G. C. Greubel, <a href="/A248725/b248725.txt">Table of n, a(n) for n = 0..10000</a>
%F A248725 Equals Sum_{k>=1} d(k)/8^k, where d(k) is the number of divisors of k (A000005). - _Amiram Eldar_, Jun 22 2020
%e A248725 0.16096618431506239680530256414364288555074385602532834636083591864782394085800...
%p A248725 evalf(sum(1/(8^k-1), k=1..infinity),120) # _Vaclav Kotesovec_, Oct 18 2014
%p A248725 # second program with faster converging series
%p A248725 evalf( add( (1/8)^(n^2)*(1 + 2/(8^n - 1)), n = 1..10), 105); # _Peter Bala_, Jan 30 2022
%t A248725 x = 1/8; RealDigits[ Sum[ DivisorSigma[0, k] x^k, {k, 1000}], 10, 105][[1]] (* after an observation and the formula of _Amarnath Murthy_, see A073668 *)
%o A248725 (PARI) suminf(k=1, 1/(8^k-1)) \\ _Michel Marcus_, Oct 18 2014
%Y A248725 Cf. A000005, A065442, A073668, A214369, A248721, A248722, A248723, A248724, A248726.
%K A248725 nonn,cons
%O A248725 0,2
%A A248725 _Robert G. Wilson v_, Oct 12 2014