A163374 a(n) = tau(tau(phi(n))).

1, 1, 2, 2, 2, 2, 3, 2, 3, 2, 3, 2, 4, 3, 3, 3, 2, 3, 4, 3, 4, 3, 3, 3, 4, 4, 4, 4, 4, 3, 4, 2, 4, 2, 4, 4, 3, 4, 4, 2, 4, 4, 4, 4, 4, 3, 3, 2, 4, 4, 4, 4, 4, 4, 4, 4, 3, 4, 3, 2, 6, 4, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 6, 3, 4, 3, 6, 4, 4, 4, 4, 4, 3, 4, 2, 4

Offset: 1

Author

Jaroslav Krizek, Jul 25 2009

Keywords

• nonn
• easy

Examples

			tau(tau(phi(7))) = tau(tau(6)) = tau(4) = 3. Thus a(7) = 3. - _Derek Orr_, Jul 27 2014
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000005 (tau), A000010 (phi), A010553, A062821.

Programs

Magma

[NumberOfDivisors(NumberOfDivisors(EulerPhi(n))): n in [1..100]]; // Vincenzo Librandi, Jul 27 2014

Mathematica

DivisorSigma[0,DivisorSigma[0,EulerPhi[Range[90]]]] (* Harvey P. Dale, Mar 25 2016 *)

PARI

a(n)=sigma(sigma(eulerphi(n),0),0); \\ Derek Orr, Jul 27 2014

Formula

a(n) = A000005(A000005(A000010(n))) = A000005(A062821(n)) = A010553(A000010(n)).

Extensions

More terms from Vincenzo Librandi, Jul 27 2014