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 A078551 #9 Aug 01 2019 11:32:21 %S A078551 5,5,7,13,5,5,17,13,13,61,7,17,5,13,31,29,13,181,13,5,61,53,17,31,17, %T A078551 41,7,421,13,37,13,61,29,13,13,137,181,17,17,29,5,37,61,13,53,17,31, %U A078551 43,31,29,17,281,41,61,17,181,421,1741,13,1861,37,13,127,17,61,449,29,53 %N A078551 Largest prime dividing sigma(2,n). %H A078551 Amiram Eldar, <a href="/A078551/b078551.txt">Table of n, a(n) for n = 2..10000</a> %F A078551 a(n) = A006530(A001157(n)). %t A078551 gpf[n_] := FactorInteger[n][[-1, 1]]; a[n_] := gpf[DivisorSigma[2, n]]; Array[a, 70, 2] (* _Amiram Eldar_, Aug 01 2019 *) %Y A078551 Cf. A006530, A001157-A001160, A071190. %K A078551 nonn %O A078551 2,1 %A A078551 _Labos Elemer_, Dec 05 2002