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 A117920 #16 Feb 16 2025 08:33:00
%S A117920 1,2,1,3,1,4,2,2,5,3,2,6,4,2,3,7,5,3,3,8,6,4,3,9,4,7,5,3,10,4,8,6,4,
%T A117920 11,4,9,5,7,5,12,4,10,5,8,6,13,4,11,5,9,6,7,14,5,12,5,10,6,8,15,6,13,
%U A117920 5,11,6,9,16,7,7,14,5,12,6,10,17,7,8,15,6,13,6,11,18,7,9,16,8,7,14,6,12,19
%N A117920 Number of digits in the decimal expansion of the regular unit fractions 1/A003592.
%H A117920 Amiram Eldar, <a href="/A117920/b117920.txt">Table of n, a(n) for n = 2..10000</a>
%H A117920 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/RegularNumber.html">Regular Number</a>
%e A117920 1/A003592(2) = 1/2 = 0.5, with 1 digit after the decimal point, so a(2) = 1.
%t A117920 digNum[n_] := Length[(dig = RealDigits[1/n,10])[[1]]] - dig[[2]]; s = {}; m = 12; Do[n = 5^k; While[n <= 5^m, AppendTo[s, n]; n *= 2], {k, 0, m}]; Rest[digNum /@ Union[s]] (* _Amiram Eldar_, Feb 08 2020 *)
%Y A117920 Cf. A003592.
%K A117920 nonn,base
%O A117920 2,2
%A A117920 _Eric W. Weisstein_, Apr 02 2006
%E A117920 Offset corrected by _Amiram Eldar_, Feb 08 2020