cp's OEIS Frontend

A342668 Largest prime in the denominator of ratio A341528(n)/A341529(n) (when presented in its lowest terms).

%I A342668 #10 Mar 28 2021 15:53:28
%S A342668 1,3,5,7,7,5,11,3,13,7,13,7,17,11,7,31,19,13,23,7,11,13,29,5,31,17,5,
%T A342668 11,31,7,37,3,13,19,11,7,41,23,17,7,43,11,47,3,13,29,53,31,11,31,19,
%U A342668 17,59,5,13,11,23,31,61,7,67,37,13,127,17,13,71,19,29,11,73,13,79,41,31,23,13,17,83,31,11,43,89,11
%N A342668 Largest prime in the denominator of ratio A341528(n)/A341529(n) (when presented in its lowest terms).
%H A342668 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>
%H A342668 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%F A342668 a(n) = A006530(A341527(n)).
%o A342668 (PARI)
%o A342668 A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };
%o A342668 A006530(n) = if(n>1, vecmax(factor(n)[, 1]), 1);
%o A342668 A341527(n) = { my(s=A003961(n)); denominator((sigma(s)*n)/(sigma(n)*s)); };
%o A342668 A342668(n) = A006530(A341527(n));
%Y A342668 Cf. A000203, A003961, A006530, A341527, A341528, A341529, A342667.
%Y A342668 Cf. A341628 (same sequence applied onto prime shift array A246278).
%K A342668 nonn
%O A342668 1,2
%A A342668 _Antti Karttunen_, Mar 24 2021