A009213 a(n) = gcd(d(n), phi(n)), where d is the number of divisors of n (A000005) and phi is Euler's totient function (A000010).

1, 1, 2, 1, 2, 2, 2, 4, 3, 4, 2, 2, 2, 2, 4, 1, 2, 6, 2, 2, 4, 2, 2, 8, 1, 4, 2, 6, 2, 8, 2, 2, 4, 4, 4, 3, 2, 2, 4, 8, 2, 4, 2, 2, 6, 2, 2, 2, 3, 2, 4, 6, 2, 2, 4, 8, 4, 4, 2, 4, 2, 2, 6, 1, 4, 4, 2, 2, 4, 8, 2, 12, 2, 4, 2, 6, 4, 8, 2, 2, 1, 4, 2, 12, 4, 2, 4, 8, 2, 12, 4, 2, 4, 2, 4, 4, 2, 6, 6, 1, 2, 8, 2, 8, 8

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Links

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

Crossrefs

Cf. A000005, A000010,

Cf. also A009191, A009195, A009223, A318459.

Programs

Mathematica

Table[GCD[DivisorSigma[0,n],EulerPhi[n]],{n,110}] (* Harvey P. Dale, May 12 2025 *)

PARI

A009213(n) = gcd(numdiv(n), eulerphi(n)); \\ Antti Karttunen, Sep 07 2018