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 A171928 #20 Jan 28 2022 07:48:17 %S A171928 3,6,487,1461,4383,13149,56598313,169794939 %N A171928 Numbers k which divide the periodic part of the decimal expansion of 1/k. %C A171928 There are two definitions of the periodic part: zeros may either begin or end the periodic part. For example, for 1/11 = 0.0909090..., the periodic part could be either 09 or 90. This sequence assumes that the zeros are at the beginning of the periodic part. See A179267 for the case of zeros at the end of the periodic part. The prime numbers in this sequence are in A045616. The three numbers following 487 are 3*487, 9*487, and 27*487. There are no other multiples of 487 here because 3 and 487 are the only prime factors of 10^486-1 that occur to a power greater than 1. - _T. D. Noe_, Jul 06 2010 %H A171928 Helmut Richter, <a href="http://www.lrz-muenchen.de/~hr/numb/fact486.html">Factors of 10^486-1</a> %e A171928 6 is a term because 1/6 = 0.166666... has periodic part 6, which is divisible by 6. %Y A171928 Cf. A045616, A179267. %K A171928 nonn,base,more %O A171928 1,1 %A A171928 _Zhining Yang_, Jan 05 2010 %E A171928 Example shortened by _T. D. Noe_, Jun 27 2010 %E A171928 Extended by _T. D. Noe_, Jul 06 2010