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 A102380 #42 Aug 02 2024 11:32:41 %S A102380 1,11,3,37,11,101,41,271,3,7,11,13,37,239,4649,11,73,101,137,3,3,37, %T A102380 333667,11,41,271,9091,21649,513239,3,7,11,13,37,101,9901,53,79, %U A102380 265371653,11,239,4649,909091,3,31,37,41,271,2906161,11,17,73,101 %N A102380 Irregular triangle read by rows in which row n lists prime factors (with multiplicity) of the repunit (10^n - 1)/9 (A002275(n)). %C A102380 See A003020 for other links and references. %H A102380 <a href="/A102380/b102380.txt">Rows n=1..352, flattened</a> %H A102380 Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorizations of 11...11 (repunit)</a>. %H A102380 Yousuke Koide, <a href="https://repunit-koide.jimdofree.com/">Factorizations of Repunit Numbers</a> %H A102380 Franz Lemmermeyer, <a href="https://arxiv.org/abs/1201.0282">Simerka - Quadratic Forms and Factorization</a>, arXiv:1201.0282 [math.NT], 2011. For the 19th row = [2071723, 5363222357]. %H A102380 Samuel Yates, <a href="http://www.jstor.org/stable/2689643">The Mystique of Repunits</a>, Math. Mag. 51 (1978), 22-28. %e A102380 First rows: %e A102380 1; %e A102380 11; %e A102380 3, 37; %e A102380 11, 101; %e A102380 41, 271; %e A102380 3, 7, 11, 13, 37; %e A102380 239, 4649; %e A102380 ... %p A102380 [seq( ifactor((10^n-1)/9),n=1..20)]; %Y A102380 Cf. A002275, A067063, A003020, A204845, A204846, A204847, A204848. %K A102380 nonn,tabf %O A102380 1,2 %A A102380 _N. J. A. Sloane_, Nov 28 2006 %E A102380 First 100 rows in b-file from _T. D. Noe_, Feb 27 2009 %E A102380 Rows n=101..322 in b-file from _Ray Chandler_, May 01 2017 %E A102380 Rows n=323..352 in b-file from _Max Alekseyev_, Apr 26 2022