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 A121090 #9 May 05 2023 06:29:35 %S A121090 1,1,6,1,2,1,6,6,1,16,1,18,6,2,22,1,6,3,6,28,1,15,2,16,6,1,3,18,6,5,6, %T A121090 21,2,1,22,46,1,42,16,6,13,3,2,6,18,28,58,1,60,15,6,6,2,33,16,22,6,35, %U A121090 1,8,3,1,18,6,6,13,9,5,41,6,16,21,28,2,44,1,6,22,15,46,18,1,96,42,2,4,16 %N A121090 Period of unit fractions having periodic decimal expansions. %C A121090 See A007732, which is the main entry for this sequence. %F A121090 a(n) = A007732(A085837(n)). - _Kevin Ryde_, May 05 2023 %e A121090 The first unit fraction considered is 1/3 because both 1/1 and 1/2 have finite decimal expansions. %e A121090 a(1) = 1 because 1/3=.33333... whose repeating portion, 3, is of length 1. %e A121090 Note: 1/4 and 1/5 are skipped because their decimal expansions are finite. %e A121090 a(2) = 1 because 1/6=.166666... whose repeating portion, 6, is of length 1. %e A121090 a(3) = 6 because 1/7 =.142857142857... whose repeating portion, 142857, is of length 6. %Y A121090 Cf. A085837, A007732. %K A121090 nonn,base %O A121090 0,3 %A A121090 _Gil Broussard_, Aug 11 2006