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 A163109 a(n) = phi(tau(n)). 11
 1, 1, 1, 2, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 4, 1, 2, 1, 2, 2, 2, 1, 4, 2, 2, 2, 2, 1, 4, 1, 2, 2, 2, 2, 6, 1, 2, 2, 4, 1, 4, 1, 2, 2, 2, 1, 4, 2, 2, 2, 2, 1, 4, 2, 4, 2, 2, 1, 4, 1, 2, 2, 6, 2, 4, 1, 2, 2, 4, 1, 4, 1, 2, 2, 2, 2, 4, 1, 4, 4, 2, 1, 4, 2, 2, 2, 4, 1, 4, 2, 2, 2, 2, 2, 4, 1, 2, 2, 6, 1, 4, 1, 4, 4 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A000010(A000005(n)). - Charles R Greathouse IV, Aug 11 2009 a(1) = 1, a(p) = 1 for p = primes (A000040), a(pq) = 2 for pq = product of two distinct primes (A006881), a(pq...z) = 2^(k-1) for pq...z = product of k (k > 2) distinct primes p, q, ..., z (A120944), a(p^(q-1) = q - 1 for p, q = primes (A000040). EXAMPLE a(16) = a(2^(5-1)) = 5-1 = 4. MATHEMATICA Table[EulerPhi[DivisorSigma[0, n]], {n, 1, 80}] (* Carl Najafi, Aug 15 2011 *) PROG (PARI) a(n) = eulerphi(numdiv(n)); \\ Michel Marcus, Aug 22 2015 CROSSREFS Cf. A000005, A000010, A062821, A163377, A163378, A163379. Sequence in context: A163377 A290085 A322867 * A286574 A329320 A316112 Adjacent sequences:  A163106 A163107 A163108 * A163110 A163111 A163112 KEYWORD nonn,easy AUTHOR Jaroslav Krizek, Jul 20 2009 EXTENSIONS More terms from Carl Najafi, Aug 15 2011 Further extended by Antti Karttunen, Jul 23 2017 STATUS approved

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Last modified August 7 17:02 EDT 2020. Contains 336277 sequences. (Running on oeis4.)