cp's OEIS Frontend

A133133 a(n) is the largest prime factor of the sum of the largest prime factors of numbers from 2 to n.

%I A133133 #12 Feb 01 2025 13:38:47
%S A133133 2,5,7,3,5,11,3,3,2,43,23,59,11,71,73,5,31,7,13,31,5,79,23,83,179,13,
%T A133133 7,109,223,127,2,89,71,97,7,331,7,11,23,409,13,17,47,19,83,109,137,37,
%U A133133 7,577,59,643,19,73,83,683,89,257,97,31,31,7,877,89,53,11,197,7,29,181,11
%N A133133 a(n) is the largest prime factor of the sum of the largest prime factors of numbers from 2 to n.
%H A133133 Robert Israel, <a href="/A133133/b133133.txt">Table of n, a(n) for n = 2..10000</a>
%e A133133 a(11) = gpf(43) = 43;
%e A133133 a(12) = gpf(46) = 23.
%p A133133 gpf:= proc(n) max(numtheory:-factorset(n)) end proc:
%p A133133 map(gpf, ListTools:-PartialSums(map(gpf, [$2..100])));
%t A133133 FactorInteger[#][[-1,1]]&/@Accumulate[Table[FactorInteger[n][[-1,1]],{n,2,80}]] (* _Harvey P. Dale_, Feb 01 2025 *)
%o A133133 (PARI) gpf(n) = vecmax(factor(n)[,1]);
%o A133133 a(n) = gpf(sum(k=2, n, gpf(k))); \\ _Michel Marcus_, Jun 02 2021
%Y A133133 Cf. A006530, A088822.
%K A133133 easy,nonn,look
%O A133133 2,1
%A A133133 Paul Finley (pfinley(AT)touro.edu), Sep 21 2007