A241479 GCD of the solutions x of sigma(x) = sigma(n), where sigma(n) = A000203(n) = sum of divisors of n.

1, 2, 3, 4, 5, 1, 7, 8, 9, 1, 1, 12, 13, 1, 1, 1, 1, 18, 19, 1, 1, 22, 1, 1, 1, 1, 27, 1, 29, 1, 1, 32, 1, 1, 1, 36, 37, 1, 1, 1, 1, 1, 43, 1, 45, 1, 1, 3, 49, 50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 61, 1, 1, 64, 1, 1, 67, 2, 1, 1, 1, 72, 73, 1, 3, 1, 1, 1, 1, 2

Offset

1,2

Comments

A variant of A240667 without zeros.

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

Max Alekseyev, PARI/GP Scripts for Miscellaneous Math Problems (invphi.gp).

Formula

a(n) = A240667(A000203(n)).

Example

a(6) = 1 since sigma(6) = 12 and sigma(11) = 12 and gcd(6, 11) = 1.

Prog

(PARI) sigv(n) =  select(i->sigma(i) == n, vector(n, i, i));
a(n) = gcd(sigv(sigma(n)));
(PARI) a(n) = gcd(invsigma(sigma(n))); \\ Amiram Eldar, Dec 19 2024, using Max Alekseyev's invphi.gp

Crossrefs

Cf. A000203, A240667.

Sequence in context: A059806 A332425 A286594 * A100994 A375228 A140523

Adjacent sequences: A241476 A241477 A241478 * A241480 A241481 A241482

Keyword

nonn

Author

Michel Marcus, Apr 23 2014

Status

approved