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a(n) = (n+1) / gcd(sigma(n),n+1).
4

%I #9 Jan 07 2023 13:05:48

%S 2,1,1,5,1,7,1,3,10,11,1,13,1,5,2,17,1,19,1,1,11,23,1,5,26,9,7,29,1,

%T 31,1,11,17,35,3,37,1,13,5,41,1,43,1,15,23,47,1,49,50,17,13,53,1,11,7,

%U 19,29,59,1,61,1,21,8,65,11,67,1,23,35,71,1,73,1,25,19,11,13,79,1,27,82,83,1,85,43,29,11,89,1,7

%N a(n) = (n+1) / gcd(sigma(n),n+1).

%H Antti Karttunen, <a href="/A339966/b339966.txt">Table of n, a(n) for n = 1..65537</a>

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

%F a(n) = (n+1) / A339964(n).

%F a(n) = denominator(sigma(n)/(n+1)). - _Michel Marcus_, Jan 07 2023

%o (PARI) A339966(n) = (n+1)/(gcd(sigma(n),n+1));

%Y Cf. A000203, A339964, A339965 (numerators).

%Y Cf. A017666.

%Y Cf. also A160596.

%K nonn,frac

%O 1,1

%A _Antti Karttunen_, Dec 25 2020