A163368 - OEIS

A163368

a(n) = phi(sigma(tau(n))).

1, 2, 2, 2, 2, 6, 2, 6, 2, 6, 2, 4, 2, 6, 6, 2, 2, 4, 2, 4, 6, 6, 2, 8, 2, 6, 6, 4, 2, 8, 2, 4, 6, 6, 6, 12, 2, 6, 6, 8, 2, 8, 2, 4, 4, 6, 2, 6, 2, 4, 6, 4, 2, 8, 6, 8, 6, 6, 2, 12, 2, 6, 4, 4, 6, 8, 2, 4, 6, 8, 2, 12, 2, 6, 4, 4, 6, 8, 2, 6, 2, 6, 2, 12, 6

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OFFSET

1,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A000010(A000203(A000005(n))) = A000010(A062069(n)) = A062401(A000005(n)).

a(1) = 1, a(p) = 2 for p = primes (A000040), a(pq) = 6 for pq = product of two distinct primes (A006881), a(pq...z) = A000010(2^(k+1)-1) = A053287(k+1) for pq...z = product of k (k > 2) distinct primes p,q,...,z (A120944).

MAPLE

with(numtheory): A163368:=n->phi(sigma(tau(n))): seq(A163368(n), n=1..150); # Wesley Ivan Hurt, Dec 19 2016

MATHEMATICA

Table[EulerPhi[DivisorSigma[1, DivisorSigma[0, n]]], {n, 100}] (* G. C. Greubel, Dec 19 2016 *)

PROG

(PARI) vector(50, n, eulerphi(sigma(numdiv(n)))) \\ G. C. Greubel, Dec 19 2016

(Magma) [EulerPhi(SumOfDivisors(NumberOfDivisors(n))): n in [1..80]]; // Vincenzo Librandi, Dec 21 2016

CROSSREFS

Cf. A000005, A000010, A000040, A000203, A006881, A053287, A062069, A062401, A120944.

Sequence in context: A164126 A343783 A261902 * A151948 A349923 A080400

Adjacent sequences: A163365 A163366 A163367 * A163369 A163370 A163371

KEYWORD

nonn,easy

AUTHOR

Jaroslav Krizek, Jul 25 2009

STATUS

approved