login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

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