cp's OEIS Frontend

A342664 Denominator of ratio A342661(n)/A342662(n).

%I A342664 #9 Mar 28 2021 15:53:08
%S A342664 1,3,8,7,9,4,20,15,52,27,21,14,77,10,4,31,117,26,170,63,160,63,114,5,
%T A342664 279,77,64,5,115,6,464,63,28,351,6,13,589,85,308,27,777,80,902,147,26,
%U A342664 171,516,31,1425,837,104,539,423,32,189,25,1360,345,530,7,1829,232,1040,127,231,14,2074,117,304,9,1206,65,2627
%N A342664 Denominator of ratio A342661(n)/A342662(n).
%H A342664 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>
%H A342664 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%F A342664 a(n) = A342662(n) / A342670(n) = A342662(n) / gcd(A342661(n), A342662(n)).
%o A342664 (PARI)
%o A342664 A064989(n) = { my(f); f = factor(n); if((n>1 && f[1,1]==2), f[1,2] = 0); for (i=1, #f~, f[i,1] = precprime(f[i,1]-1)); factorback(f) };
%o A342664 A326041(n) = sigma(A064989(n));
%o A342664 A342661(n) = (n*A326041(n));
%o A342664 A342662(n) = (sigma(n)*A064989(n));
%o A342664 A342664(n) = { my(v=A342662(n)); (v/gcd(A342661(n),v)); };
%o A342664 \\ Alternatively as:
%o A342664 A342664(n) = denominator(A342661(n)/A342662(n));
%Y A342664 Cf. A000203, A064989, A326041, A341526 [= a(A003961(n))], A341527, A342661, A342662, A342663 (numerators), A342667 [largest prime factor of a(A003961(n))], A342670.
%K A342664 nonn,frac
%O A342664 1,2
%A A342664 _Antti Karttunen_, Mar 23 2021