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A218259 a(n) = |{m : multiplicative order of n mod m = 10}|. 2

%I

%S 0,5,16,38,47,40,66,84,150,33,72,10,106,178,168,140,265,54,534,106,68,

%T 20,296,56,564,231,732,52,730,26,604,114,80,164,348,332,297,50,912,84,

%U 904,110,88,130,222,552,332,76,1430,81,702,236,950,178,256,168,564

%N a(n) = |{m : multiplicative order of n mod m = 10}|.

%H Alois P. Heinz, <a href="/A218259/b218259.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = tau(n^10-1)-tau(n^5-1)-tau(n^2-1)+tau(n-1), with tau = A000005.

%p with(numtheory):

%p a:= n-> add(mobius(10/d) *tau(n^d-1), d={1, 2, 5, 10}):

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

%Y Row n=10 of A212957.

%Y Cf. A000005, A008683.

%K nonn

%O 1,2

%A _Alois P. Heinz_, Oct 24 2012

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Last modified July 16 09:13 EDT 2020. Contains 335784 sequences. (Running on oeis4.)