A058663 a(n) = gcd(n-1, n-phi(n)).

0, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 7, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 23, 1, 1, 1, 1, 1, 5, 1, 1, 1, 1, 1, 3, 1, 1, 21, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1

Offset: 1

Author

Labos Elemer, Dec 28 2000

Keywords

• nonn

Examples

			For n = 15; n-1 = 14, cototient(15) = 15-phi(15) = 7, a(15) = gcd(14,7) = 7; For most n-s, among others for primes a(n) = 1.
		

Links

• Antti Karttunen, Table of n, a(n) for n = 1..65537

Crossrefs

Cf. A000010, A049559, A051953, A009195.

Programs

Maple

with(numtheory); A058663:=n->igcd(n-1, n-phi(n)); seq(A058663(n), n=1..100); # Wesley Ivan Hurt, Apr 01 2014

Mathematica

Table[GCD[n - 1, n - EulerPhi[n]], {n, 100}] (* Wesley Ivan Hurt, Apr 01 2014 *)

PARI

A058663(n) = gcd(n-1, n-eulerphi(n)); \\ Antti Karttunen, Sep 25 2018

Formula

a(n) = gcd(n-1, cototient(n)) = gcd(n-1, A051953(n)).