%I #21 Sep 08 2022 08:45:49
%S 1,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,
%T 12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,
%U 3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3,9,12,6,3
%N 3^n mod 15.
%H Vincenzo Librandi, <a href="/A168400/b168400.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1, -1, 1).
%F From _R. J. Mathar_, Apr 13 2010: (Start)
%F a(n) = a(n-1) -a(n-2) +a(n-3), n>3.
%F G.f.: (1 + 2*x + 7*x^2 + 5*x^3)/((1-x)*(1+x^2)). (End)
%t Table[Mod[3^n,15], {n,0,50}] (* _G. C. Greubel_, Jul 21 2016 *)
%o (Sage) [power_mod(3, n, 15) for n in range(0, 90)]
%o (PARI) a(n)=lift(Mod(3,15)^n) \\ _Charles R Greathouse IV_, Mar 22 2016
%o (Magma) [Modexp(3, n, 15): n in [0..110]]; // _Vincenzo Librandi_, Jul 21 2016
%K nonn,easy
%O 0,2
%A _Zerinvary Lajos_, Nov 25 2009
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