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%I #33 Dec 25 2023 13:46:35
%S 1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,
%T 13,9,17,1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,13,9,17,
%U 1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,13,9,17,1,5,25,13,9
%N a(n) = 5^n mod 28.
%H Edward Jiang, <a href="/A070378/b070378.txt">Table of n, a(n) for n = 0..10000</a>
%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,-1,1,-1,1).
%F From _R. J. Mathar_, Apr 20 2010: (Start)
%F a(n) = a(n-1) - a(n-2) + a(n-3) - a(n-4) + a(n-5).
%F G.f.: ( -1-4*x-21*x^2+8*x^3-17*x^4 ) / ( (x-1)*(1+x+x^2)*(1-x+x^2) ). (End)
%F a(n) = a(n-6). - _G. C. Greubel_, Mar 13 2016
%t PowerMod[5, Range[0, 50], 28] (* _G. C. Greubel_, Mar 13 2016 *)
%o (Sage) [power_mod(5,n,28) for n in range(0,83)] # _Zerinvary Lajos_, Nov 26 2009
%o (PARI) a(n)=lift(Mod(5,28)^n) \\ _Charles R Greathouse IV_, Mar 22 2016
%K nonn,easy
%O 0,2
%A _N. J. A. Sloane_, May 12 2002
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