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 A087020 #26 Feb 16 2025 08:32:50 %S A087020 37,5882353,333667,513239,121499449,11111111111111111111111, %T A087020 154083204930662557781201849,39526741,9999999900000001, %U A087020 59779577156334533866654838281,119968369144846370226083377,8396862596258693901610602298557167100076327481 %N A087020 Greatest prime factor of n-th cyclic number. %C A087020 A004042(n) factorized with Dario Alpern's ECM. %C A087020 Extended using factors of 10^(A001913(n)-1)-1, see Kamada link. %H A087020 Max Alekseyev, <a href="/A087020/b087020.txt">Table of n, a(n) for n = 1..51</a> (first 42 terms from Ray Chandler) %H A087020 Dario A. Alpern, <a href="https://www.alpertron.com.ar/ECM.HTM">Factorization using the Elliptic Curve Method</a>. %H A087020 Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/">Factorizations of 11...11 (Repunit)</a> %H A087020 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CyclicNumber.html">Cyclic Number</a> %F A087020 a(n) = A006530(A004042(n+1)). %e A087020 A004042(2) = 142857 = 37*13*11*3^3, therefore a(1) = 37. %Y A087020 Cf. A001913, A087021, A087022, A087023, A087024, A087025, A087026. %K A087020 nonn %O A087020 1,1 %A A087020 _Reinhard Zumkeller_, Jul 30 2003 %E A087020 a(12) from _Ray Chandler_, Nov 16 2011