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 A001270 #26 May 23 2023 22:59:24
%S A001270 3,3,3,3,11,3,3,3,37,3,3,11,101,3,3,41,271,3,3,3,7,11,13,37,3,3,239,
%T A001270 4649,3,3,11,73,101,137,3,3,3,3,37,333667,3,3,11,41,271,9091,3,3,
%U A001270 21649,513239,3,3,3,7,11,13,37,101,9901,3,3,53,79,265371653
%N A001270 Table of prime factors of 10^n - 1 (with multiplicity).
%C A001270 The length of the n-th row is A057951(n).
%D A001270 J. Brillhart et al., Factorizations of b^n +- 1. Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 2nd edition, 1985; and later supplements.
%H A001270 Max Alekseyev, <a href="/A001270/b001270.txt">Rows n = 1..352, flattened</a>
%H A001270 J. Brillhart et al., <a href="http://dx.doi.org/10.1090/conm/022">Factorizations of b^n +- 1</a>, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
%H A001270 Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit">Factorizations of 11...11 (Repunit)</a>.
%H A001270 S. S. Wagstaff, Jr., <a href="http://www.cerias.purdue.edu/homes/ssw/cun/index.html">The Cunningham Project</a>
%t A001270 Table[f = FactorInteger[10^n - 1]; Flatten[Table[Table[i[[1]], {i[[2]]}], {i, f}]], {n, 13}] (* _T. D. Noe_, Jun 27 2012 *)
%Y A001270 Cf. A002283.
%K A001270 nonn,tabf
%O A001270 1,1
%A A001270 _N. J. A. Sloane_
%E A001270 Erroneous b-file replaced by _Ray Chandler_, Apr 26 2017
%E A001270 b-file corrected and extended with rows 323..352 by _Max Alekseyev_, May 23 2023