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

1,10

Links

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

Formula

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

Example

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.

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 *)

Prog

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

Crossrefs

Cf. A000010, A049559, A051953, A009195.

Sequence in context: A010122 A220693 A208615 * A124371 A147989 A119329

Adjacent sequences: A058660 A058661 A058662 * A058664 A058665 A058666

Keyword

nonn

Author

Labos Elemer, Dec 28 2000

Status

approved