A058656 a(n) = gcd(n+1, phi(n)).

1, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 3, 8, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 3, 2, 1, 2, 1, 2, 1, 2, 1, 12, 1, 2, 3, 8, 1, 2, 1, 2, 5, 2, 1, 2, 1, 2, 1, 4, 1, 2, 1, 8, 3, 2, 1, 2, 1, 2, 3, 4, 1, 6, 1, 2, 1, 2, 1, 2, 1, 2, 3, 4, 1, 6, 1, 2, 1, 2, 1, 2, 1, 2, 3, 8, 1, 2, 1, 4, 1, 2, 1, 24, 1, 2, 3, 20, 1, 2, 1

Offset

1,3

Comments

Compare sequences gcd(x, phi(n)), where x = n-1, n, or n+1.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Example

For n = 12, 13, 14, 15: n+1 = 13, 14, 15, 16; phi(n) = 4, 12, 12, 8; a(n) = gcd(13,4), gcd(14,12), gcd(15,12), gcd(16,8) = 1, 2, 3, 8, respectively.

Mathematica

Table[GCD[n+1, EulerPhi[n]], {n, 110}] (* Harvey P. Dale, Nov 17 2011 *)

Prog

(PARI) a(n) = gcd(n+1, eulerphi(n)); \\ Amiram Eldar, Mar 13 2025

Crossrefs

Cf. A000010, A009195, A058515.

Sequence in context: A161302 A161277 A160981 * A184221 A373531 A226898

Adjacent sequences: A058653 A058654 A058655 * A058657 A058658 A058659

Keyword

nonn,changed

Author

Labos Elemer, Dec 28 2000

Extensions

Offset corrected by Sean A. Irvine, Aug 11 2022

Status

approved