A318827 a(n) = n - gcd(n - 1, phi(n)).

0, 1, 1, 3, 1, 5, 1, 7, 7, 9, 1, 11, 1, 13, 13, 15, 1, 17, 1, 19, 17, 21, 1, 23, 21, 25, 25, 25, 1, 29, 1, 31, 29, 33, 33, 35, 1, 37, 37, 39, 1, 41, 1, 43, 41, 45, 1, 47, 43, 49, 49, 49, 1, 53, 53, 55, 53, 57, 1, 59, 1, 61, 61, 63, 49, 61, 1, 67, 65, 67, 1, 71, 1, 73, 73, 73, 73, 77, 1, 79, 79, 81, 1, 83, 81, 85, 85, 87, 1, 89, 73

Offset: 1

Author

Antti Karttunen, Sep 09 2018

Keywords

• nonn

Comments

a(n) = n-1 for n in A209211.

Links

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

Crossrefs

Cf. A000010, A051953, A049559, A209211, A318828, A318829, A318830.

Programs

Mathematica

Array[# - GCD[# - 1, EulerPhi[#]] &, 100] (* Alonso del Arte, Sep 09 2018 *)

PARI

A318827(n) = (n-gcd(eulerphi(n), n-1));

Formula

a(n) = n - A049559(n) = n - gcd(n - 1, phi(n)).

a(n) = A051953(n) + A318830(n).

a(p) = 1 for p prime.