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 A260234 #11 Feb 23 2020 07:08:29 %S A260234 3,5,7,5,11,13,5,17,19,11,23,13,7,29,31,17,7,37,13,41,43,23,47,7,17, %T A260234 53,11,29,59,61,7,13,67,23,71,73,19,13,79,41,83,43,29,89,23,47,19,97, %U A260234 11,101,103,53,107,109,37,113,29,59,17,61,41,7,127,43,131 %N A260234 Largest prime factor of the n-th hexagonal number (A000384). %C A260234 As A000384(n+1) = (n*2+1)*(n*1+1), A000384(n) belongs to A180045 for n > 3, and a(n) tends to infinity as n tends to infinity. - _Rémy Sigrist_, Feb 23 2020 %H A260234 Colin Barker, <a href="/A260234/b260234.txt">Table of n, a(n) for n = 2..1000</a> %F A260234 a(n) = A006530(A000384(n)). %e A260234 a(3) = 5 because A000384(3) = 15 = 3 * 5. %t A260234 FactorInteger[#][[-1,1]]&/@PolygonalNumber[6,Range[2,70]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Apr 10 2018 *) %o A260234 (PARI) %o A260234 pg(m, n) = (n^2*(m-2)-n*(m-4))/2 \\ n-th m-gonal number %o A260234 lpf(m) = vecmax(factorint(m)[, 1]) \\ Largest prime factor %o A260234 a(n) = lpf(pg(6, n)) %Y A260234 Cf. A000384, A006530, A180045, A260233, A260235, A260236. %K A260234 nonn %O A260234 2,1 %A A260234 _Colin Barker_, Jul 20 2015