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 A163109 phi(tau(n)) 9
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS a(n) = A000010(A000005(n)) - Charles R Greathouse IV Aug 11 2009 LINKS FORMULA 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 *) CROSSREFS Sequence in context: A082477 A036430 A163377 * A128428 A056171 A076755 Adjacent sequences:  A163106 A163107 A163108 * A163110 A163111 A163112 KEYWORD nonn,easy AUTHOR Jaroslav Krizek, Jul 20 2009 EXTENSIONS More terms by Carl Najafi, Aug 15 2011 STATUS approved

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