%I #24 Dec 18 2023 14:29:55
%S 1,3,9,2,6,18,4,12,11,8,24,22,16,23,19,7,21,13,14,17,1,3,9,2,6,18,4,
%T 12,11,8,24,22,16,23,19,7,21,13,14,17,1,3,9,2,6,18,4,12,11,8,24,22,16,
%U 23,19,7,21,13,14,17,1,3,9,2,6,18,4,12,11,8,24,22,16
%N a(n) = 3^n mod 25.
%H G. C. Greubel, <a href="/A070343/b070343.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_11">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 0, 0, 0, 0, 0, 0, 0, -1, 1).
%F From _R. J. Mathar_, Apr 13 2010: (Start)
%F a(n) = a(n-1) - a(n-10) + a(n-11).
%F G.f.: (1+2*x+6*x^2-7*x^3+4*x^4+12*x^5-14*x^6+8*x^7-x^8-3*x^9+17*x^10)/ ((1-x) * (x ^2+1) * (x^8-x^6+x^4-x^2+1)). (End)
%F a(n) = a(n-20). - _G. C. Greubel_, Mar 12 2016
%t PowerMod[3, Range[0, 50], 25] (* _G. C. Greubel_, Mar 12 2016 *)
%o (Sage) [power_mod(3,n,25)for n in range(0, 73)] # _Zerinvary Lajos_, Nov 25 2009
%o (PARI) a(n)=lift(Mod(3,25)^n) \\ _Charles R Greathouse IV_, Mar 22 2016
%K nonn,easy
%O 0,2
%A _N. J. A. Sloane_, May 12 2002