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%I #42 Dec 27 2023 08:37:31
%S 1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,
%T 13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,
%U 7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1,7,4,13,1
%N a(n) = 7^n mod 15.
%H G. C. Greubel, <a href="/A070406/b070406.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1).
%F From _R. J. Mathar_, Apr 20 2010: (Start)
%F a(n) = a(n-4).
%F G.f.: ( -1 - 7*x - 4*x^2 - 13*x^3 ) / ( (x-1)*(1+x)*(1+x^2) ). (End)
%F E.g.f.: (1/2)*(5*cosh(x) + 20*sinh(x) - 3*cos(x) - 6*sin(x)). - _G. C. Greubel_, Mar 20 2016
%t PowerMod[7, Range[0, 50], 15] (* _G. C. Greubel_, Mar 20 2016 *)
%t LinearRecurrence[{0,0,0,1},{1,7,4,13},100] (* or *) PadRight[{},100,{1,7,4,13}] (* _Harvey P. Dale_, Oct 13 2018 *)
%o (Sage) [power_mod(7,n,15) for n in range(0,93)] # _Zerinvary Lajos_, Nov 27 2009
%o (PARI) a(n) = lift(Mod(7, 15)^n); \\ _Altug Alkan_, Mar 20 2016
%o (Magma) [Modexp(7, n, 15): n in [0..100]]; // _Bruno Berselli_, Mar 22 2016
%K nonn,easy
%O 0,2
%A _N. J. A. Sloane_, May 12 2002
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