A353751 a(n) = gcd(n, sigma(sigma(n))), where sigma is the sum of divisors function.

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

Author

Antti Karttunen, May 08 2022

Keywords

• nonn

Links

• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A051027, A318059, A318060.

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

Cf. also A009194, A295310.

Programs

PARI

A353751(n) = gcd(n, sigma(sigma(n)));

Formula

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

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