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URL: https://oeis.org/A353751

⇱ A353751 - OEIS

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A353751
a(n) = gcd(n, sigma(sigma(n))), where sigma is the sum of divisors function.
1
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, 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, 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
OFFSET
1,2
FORMULA
a(n) = gcd(n, A051027(n)).
a(n) = A051027(n) / A318059(n) = n / A318060(n).
PROG
(PARI) A353751(n) = gcd(n, sigma(sigma(n)));
CROSSREFS
Cf. A019278 (positions of fixed points, where a(n)=n).
Cf. also A009194, A295310.
Sequence in context: A068057 A376645 A335852 * A003484 A118827 A118830
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 08 2022
STATUS
approved