A059890 - OEIS

A059890

a(n) = |{m : multiplicative order of 8 mod m=n}|.

2, 4, 2, 18, 6, 24, 10, 72, 4, 84, 14, 462, 14, 128, 54, 672, 30, 124, 14, 4494, 82, 364, 14, 7608, 120, 172, 56, 9054, 62, 3920, 6, 5376, 238, 1500, 1518, 9600, 62, 364, 494, 69048, 30, 5892, 30, 24174, 956, 364, 62, 253280, 52, 12072, 222, 147246, 254, 12072

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OFFSET

1,1

COMMENTS

The multiplicative order of a mod m, gcd(a,m)=1, is the smallest natural number d for which a^d = 1 (mod m). a(n) = number of orders of degree-n monic irreducible polynomials over GF(8).

Also, number of primitive factors of 8^n - 1. - Max Alekseyev, May 03 2022

LINKS

Max Alekseyev, Table of n, a(n) for n = 1..500

FORMULA

a(n) = Sum_{ d divides n } mu(n/d)*tau(8^d-1), (mu(n) = Moebius function A008683, tau(n) = number of divisors of n A000005).

MAPLE

with(numtheory):

a:= n-> add(mobius(n/d)*tau(8^d-1), d=divisors(n)):

seq(a(n), n=1..40); # Alois P. Heinz, Oct 12 2012

CROSSREFS

Number of primitive factors of b^n - 1: A059499 (b=2), A059885(b=3), A059886 (b=4), A059887 (b=5), A059888 (b=6), A059889 (b=7), this sequence (b=8), A059891 (b=9), A059892 (b=10).

Cf. A000005, A008683, A027380, A053451, A057953, A058946, A274908.

Column k=8 of A212957.

Sequence in context: A227924 A100944 A295390 * A295640 A210457 A006496

Adjacent sequences: A059887 A059888 A059889 * A059891 A059892 A059893

KEYWORD

nonn

AUTHOR

Vladeta Jovovic, Feb 06 2001

STATUS

approved