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

Author

Labos Elemer, Dec 28 2000

Keywords

• nonn

Comments

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

Examples

			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.
		

Links

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

Crossrefs

Cf. A000010, A009195, A058515.

Programs

Mathematica

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

PARI

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

Extensions

Offset corrected by Sean A. Irvine, Aug 11 2022