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a(n) = (3^n-1)/2 mod n.
2

%I #13 May 19 2020 19:13:02

%S 0,0,1,0,1,4,1,0,4,4,1,4,1,4,13,0,1,4,1,0,13,4,1,16,21,4,13,12,1,4,1,

%T 0,13,4,23,4,1,4,13,0,1,28,1,40,31,4,1,16,15,24,13,40,1,40,33,32,13,4,

%U 1,40,1,4,13,0,56,34,1,40,13,54,1,40,1,4,28,40,37,52,1,0,40,4,1,28,36,4,13,24

%N a(n) = (3^n-1)/2 mod n.

%H Antti Karttunen, <a href="/A094918/b094918.txt">Table of n, a(n) for n = 1..16384</a>

%H Antti Karttunen, <a href="/A094918/a094918.txt">Data supplement: n, a(n) computed for n = 1..65537</a>

%o (PARI) A094918(n) = lift(Mod((3^n-1)/2,n)); \\ _Antti Karttunen_, May 19 2020

%Y (k^n-1)/(k-1) mod n for k = 1, ..., 10 gives A082495, this sequence, A094919, A094920, A094921, A094922, A094923, A094924 and A095250.

%Y Cf. A003462.

%K nonn,look

%O 1,6

%A _N. J. A. Sloane_, Jun 18 2004