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a(n) = gcd(n, sigma(sigma(n))), where sigma is the sum of divisors function.
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%I #13 May 08 2022 10:34:39

%S 1,2,1,4,1,2,1,8,1,1,1,4,1,2,15,16,1,2,1,4,21,1,1,24,1,2,9,4,1,15,1,8,

%T 1,2,1,4,1,2,3,2,1,42,1,4,3,1,1,16,1,2,3,1,1,18,5,8,3,2,1,60,1,2,21,

%U 64,1,1,1,4,3,1,1,24,1,2,1,4,7,6,1,16,1,2,1,84,5,2,3,2,1,6,1,4,3,1,5,8,1,2,1,4

%N a(n) = gcd(n, sigma(sigma(n))), where sigma is the sum of divisors function.

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

%F a(n) = gcd(n, A051027(n)).

%F a(n) = A051027(n) / A318059(n) = n / A318060(n).

%o (PARI) A353751(n) = gcd(n, sigma(sigma(n)));

%Y Cf. A000203, A051027, A318059, A318060.

%Y Cf. A019278 (positions of fixed points, where a(n)=n).

%Y Cf. also A009194, A295310.

%K nonn

%O 1,2

%A _Antti Karttunen_, May 08 2022