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 A197224 #15 Nov 16 2023 19:03:18
%S A197224 0,1,4,3,2,3,8,5,5,5,5,9,8,6,16,5,8,6,10,16,4,6,9,17,20,21,18,10,13,
%T A197224 19,7,27,9,30,9,12,20,30,36,20,41,23,42,41,6
%N A197224 Exponent in the power of 2 which is the period of the decimal fraction 1/A072982(n).
%C A197224 This means that the fraction 1/52613349377 repeats every 2^30 terms!
%C A197224 Every term with value up to 6 is accounted for.
%H A197224 Hans Riesel, <a href="http://www.ams.org/journals/mcom/1969-23-106/S0025-5718-1969-0245507-6/">Some factors of the numbers Gn = 6^2^n+1 and Hn = 10^2^n+1,</a> Math. Comp. 23 (1969), pp. 413-415. With errata reported in Math. Comp. 24 (1970), p. 243.
%F A197224 a(n+1) = A274512(n) + 1. - _Ray Chandler_, Oct 25 2019
%t A197224 Table[Log[2, MultiplicativeOrder[10, p]], {p, A072982}] (* _Ray Chandler_, Oct 25 2019 *)
%Y A197224 Cf. A072982, A274512.
%K A197224 nonn,base,hard,more
%O A197224 1,3
%A A197224 _T. D. Noe_, Oct 21 2011
%E A197224 a(37)-a(39) from _Ray Chandler_, Nov 03 2011
%E A197224 a(40)-a(45) from _Ray Chandler_, Oct 25 2019