A353805 - OEIS

%I #9 May 09 2022 11:02:47

%S 1,1,1,1,1,1,1,1,1,13,1,1,1,1,5,1,1,1,1,1,3,13,1,1,1,1,1,1,1,65,1,1,

%T 31,10,31,1,1,1,5,13,1,3,1,1,1,13,1,1,1,1,5,57,1,1,65,1,31,13,1,5,1,1,

%U 1,1,7,403,1,1,3,403,1,1,1,1,1,1,3,5,1,1,1,13,1,3,70,1,5,13,1,13,31,1,85,13,5,1,1,13

%N a(n) = A051027(n) / gcd(A051027(n), A353802(n)), where A051027(n) = sigma(sigma(n)), and A353802(n) = Product_{p^e||n} sigma(sigma(p^e)).

%C Denominator of fraction A353802(n) / A051027(n).

%H Antti Karttunen, <a href="/A353805/b353805.txt">Table of n, a(n) for n = 1..20000</a>

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

%F a(n) = A051027(n) / A353804(n).

%o (PARI)

%o A051027(n) = sigma(sigma(n));

%o A353805(n) = { my(f = factor(n)); (A051027(n) / gcd(A051027(n), prod(k=1, #f~, A051027(f[k, 1]^f[k, 2])))); };

%Y Cf. A000203, A051027, A353802, A353803, A353804, A353806 (numerators).

%Y Positions of 1's is given by the union of A336547 and A353807.

%Y Cf. also A353755, A353756.

%K nonn,frac

%O 1,10

%A _Antti Karttunen_, May 08 2022