A342667 - OEIS

%I #12 Mar 28 2021 15:53:16

%S 1,2,3,13,5,2,7,2,31,5,11,13,13,7,3,11,17,31,19,13,7,11,23,2,19,13,13,

%T 13,29,2,31,13,11,17,5,31,37,19,13,5,41,7,43,11,31,23,47,11,7,19,17,

%U 13,53,13,11,7,19,29,59,13,61,31,31,1093,13,11,67,17,23,5,71,31,73,37,19,19,7,13,79,11,71,41,83,13

%N Largest prime in the numerator of ratio A341528(n)/A341529(n) (when presented in its lowest terms).

%C Equally, largest prime in the denominator of ratio A342661(A003961(n)) / A342662(A003961(n)).

%H <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%F a(n) = A006530(A341526(n)).

%F a(n) = A006530(A342664(A003961(n))).

%o (PARI)

%o A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };

%o A006530(n) = if(n>1, vecmax(factor(n)[, 1]), 1);

%o A341526(n) = { my(s=A003961(n)); numerator((sigma(s)*n)/(sigma(n)*s)); };

%o A342667(n) = A006530(A341526(n));

%Y Cf. A000203, A003961, A006530, A064989, A341526, A341528, A341529, A326041, A342661, A342662, A342664, A342668.

%Y Cf. also A341607.

%K nonn

%O 1,2

%A _Antti Karttunen_, Mar 23 2021