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a(n) = 6^n mod 25.
1

%I #28 Dec 27 2023 08:37:10

%S 1,6,11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,

%T 11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,

%U 16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,16,21,1,6,11,16

%N a(n) = 6^n mod 25.

%H G. C. Greubel, <a href="/A070397/b070397.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,1).

%F a(n) = a(n-5). - _R. J. Mathar_, Apr 20 2010

%F G.f.: ( -1-6*x-11*x^2-16*x^3-21*x^4 ) / ((x-1)*(1+x+x^2+x^3+x^4)). - _R. J. Mathar_, Apr 20 2010

%t PowerMod[6,Range[0,80],25] (* _Harvey P. Dale_, Jul 22 2013 *)

%o (Sage) [power_mod(6,n,25)for n in range(0,79)] # _Zerinvary Lajos_, Nov 27 2009

%o (PARI) a(n) = lift(Mod(6, 25)^n); \\ _Altug Alkan_, Mar 18 2016

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_, May 12 2002