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 A078554 #12 Feb 02 2025 10:32:11 %S A078554 11,61,151,521,61,191,41,4561,521,13421,151,2411,191,521,1801,101, %T A078554 4561,2251,521,191,13421,211,61,1741,2411,1181,191,401,521,21821,331, %U A078554 13421,101,521,4561,1824841,2251,2411,521,4111,191,3341101,13421,4561,211 %N A078554 Largest prime dividing sigma(5,n). %H A078554 Amiram Eldar, <a href="/A078554/b078554.txt">Table of n, a(n) for n = 2..10000</a> %F A078554 a(n) = A006530(A001160(n)). %e A078554 Observe nontrivial frequent occurrence of several primes like 61,191,521,4561, etc. %t A078554 gpf[n_] := FactorInteger[n][[-1, 1]]; a[n_] := gpf[DivisorSigma[5, n]]; Array[a, 50, 2] (* _Amiram Eldar_, Aug 01 2019 *) %t A078554 FactorInteger[#][[-1,1]]&/@DivisorSigma[5,Range[2,50]] (* _Harvey P. Dale_, Feb 02 2025 *) %Y A078554 Cf. A006530, A001157-A001160, A071190. %K A078554 nonn %O A078554 2,1 %A A078554 _Labos Elemer_, Dec 05 2002