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 A059887 a(n) = |{m : multiplicative order of 5 mod m=n}|. 3
 3, 5, 3, 12, 9, 37, 3, 28, 18, 47, 3, 180, 3, 53, 81, 176, 9, 446, 21, 564, 39, 117, 9, 884, 180, 53, 360, 244, 21, 5959, 9, 800, 39, 111, 369, 9536, 21, 483, 39, 5476, 9, 18289, 9, 1140, 2958, 111, 3, 9424, 6, 3852, 177, 884, 21, 81048, 561, 1188, 69, 227, 9 (list; graph; refs; listen; history; text; internal format)
 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(5). LINKS FORMULA a(n) = Sum_{d|n} mu(n/d)*tau(5^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(5^d-1), d=divisors(n)): seq(a(n), n=1..50);  # Alois P. Heinz, Oct 12 2012 CROSSREFS Cf. A000005, A008683, A001692, A053447, A058945, A059499, A059885, A059886, A059888-A059892, A212485. Column k=5 of A212957. - Alois P. Heinz, Oct 12 2012 Sequence in context: A178095 A177904 A049072 * A023585 A089948 A023583 Adjacent sequences:  A059884 A059885 A059886 * A059888 A059889 A059890 KEYWORD easy,nonn AUTHOR Vladeta Jovovic, Feb 06 2001 STATUS approved

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Last modified July 17 20:45 EDT 2019. Contains 325109 sequences. (Running on oeis4.)