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A218258 a(n) = |{m : multiplicative order of n mod m = 9}|. 2
0, 2, 4, 26, 18, 12, 52, 4, 112, 12, 16, 12, 30, 12, 24, 488, 30, 24, 64, 4, 12, 78, 48, 28, 464, 12, 56, 62, 72, 12, 104, 56, 36, 52, 48, 112, 432, 28, 48, 52, 48, 24, 488, 56, 72, 288, 48, 24, 580, 6, 24, 116, 360, 44, 344, 16, 48, 104, 24, 8, 312, 44, 112 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = tau(n^9-1)-tau(n^3-1), with tau = A000005.

MAPLE

with(numtheory):

a:= n-> add(mobius(9/d) *tau(n^d-1), d={3, 9}):

seq(a(n), n=1..80);

MATHEMATICA

Table[DivisorSigma[0, n^9-1]-DivisorSigma[0, n^3-1], {n, 70}] (* Harvey P. Dale, Mar 15 2018 *)

CROSSREFS

Row n=9 of A212957.

Cf. A000005, A008683.

Sequence in context: A162126 A162118 A128774 * A186431 A129894 A028386

Adjacent sequences:  A218255 A218256 A218257 * A218259 A218260 A218261

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Oct 24 2012

STATUS

approved

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Last modified July 8 01:48 EDT 2020. Contains 335502 sequences. (Running on oeis4.)