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

1,2

Links

Table of n, a(n) for n=1..100.

Index entries for sequences related to sigma(n)

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. A000203, A051027, A318059, A318060.

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

Cf. also A009194, A295310.

Sequence in context: A068057 A376645 A335852 * A003484 A118827 A118830

Adjacent sequences: A353748 A353749 A353750 * A353752 A353753 A353754

Keyword

nonn

Author

Antti Karttunen, May 08 2022

Status

approved