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A163374
a(n) = tau(tau(phi(n))).
1
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
1,3
LINKS
FORMULA
EXAMPLE
tau(tau(phi(7))) = tau(tau(6)) = tau(4) = 3. Thus a(7) = 3. - Derek Orr, Jul 27 2014
MATHEMATICA
DivisorSigma[0, DivisorSigma[0, EulerPhi[Range[90]]]] (* Harvey P. Dale, Mar 25 2016 *)
PROG
(Magma) [NumberOfDivisors(NumberOfDivisors(EulerPhi(n))): n in [1..100]]; // Vincenzo Librandi, Jul 27 2014
(PARI) a(n)=sigma(sigma(eulerphi(n), 0), 0); \\ Derek Orr, Jul 27 2014
CROSSREFS
Cf. A000005 (tau), A000010 (phi), A010553, A062821.
Sequence in context: A329377 A010553 A262095 * A108502 A260235 A078120
KEYWORD
nonn,easy
AUTHOR
Jaroslav Krizek, Jul 25 2009
EXTENSIONS
More terms from Vincenzo Librandi, Jul 27 2014
STATUS
approved