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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 FORMULA a(n) = A000005(A000005(A000010(n))) = A000005(A062821(n)) = A010553(A000010(n)). 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, A000010, A010553, A062821. Sequence in context: A329377 A010553 A262095 * A108502 A260235 A078120 Adjacent sequences:  A163371 A163372 A163373 * A163375 A163376 A163377 KEYWORD nonn,easy AUTHOR Jaroslav Krizek, Jul 25 2009 EXTENSIONS More terms from Vincenzo Librandi, Jul 27 2014 STATUS approved

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Last modified September 19 07:08 EDT 2021. Contains 347554 sequences. (Running on oeis4.)