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A211178 Denominator of Sum_{k=1..n}(-1)^k/phi(k), where phi = A000010. 2
1, 1, 2, 1, 4, 4, 12, 3, 6, 12, 60, 30, 60, 20, 40, 20, 80, 240, 720, 720, 720, 144, 1584, 1584, 7920, 7920, 7920, 7920, 55440, 55440, 11088, 5544, 27720, 55440, 55440, 55440, 55440, 6160, 18480, 2310, 9240, 9240, 3080, 3080, 1155, 210, 2415, 38640, 5520, 5520 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

Olivier Bordell├Ęs and Benoit Cloitre, An Alternating Sum Involving the Reciprocal of Certain Multiplicative Functions, J. Int. Seq., Vol. 16 (2013) Article #13.6.3.

FORMULA

A211177(n)/a(n) = c*log(n) + O(1) with a suitable constant c (see ref).

The constant above is c = zeta(2)*zeta(3)/(3*zeta(6)) = (1/3) * A082695. - Amiram Eldar, Nov 20 2020

MATHEMATICA

Denominator @ Accumulate[Table[(-1)^k/EulerPhi[k], {k, 1, 50}]] (* Amiram Eldar, Nov 20 2020 *)

PROG

(PARI) a(n)=denominator(sum(k=1, n, (-1)^k/eulerphi(k)))

CROSSREFS

Cf. A000010, A082695, A211177 (numerators).

Sequence in context: A095293 A034409 A209478 * A048049 A212716 A057772

Adjacent sequences:  A211175 A211176 A211177 * A211179 A211180 A211181

KEYWORD

nonn,frac

AUTHOR

Benoit Cloitre, Feb 01 2013

EXTENSIONS

More terms from Amiram Eldar, Nov 20 2020

STATUS

approved

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Last modified February 25 12:00 EST 2021. Contains 341606 sequences. (Running on oeis4.)