%I #13 Dec 18 2023 17:14:53
%S 0,1,16,1,16,5,16,1,16,1,0,1,16,1,16,5,16,1,16,1,0,1,16,1,16,5,16,1,
%T 16,1,0,1,16,1,16,5,16,1,16,1,0,1,16,1,16,5,16,1,16,1,0,1,16,1,16,5,
%U 16,1,16,1,0,1,16,1,16,5,16,1,16,1,0,1,16,1,16,5,16,1,16,1,0,1,16,1,16,5,16
%N a(n) = n^4 mod 20.
%C Equivalently: n^(4*m + 4) mod 20. - _G. C. Greubel_, Apr 05 2016
%H G. C. Greubel, <a href="/A070539/b070539.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 1).
%F From _G. C. Greubel_, Apr 05 2016: (Start)
%F a(10*n) = 0.
%F a(n+10) = a(n).
%F G.f.: (x +16*x^2 +x^3 +16*x^4 +5*x^5 +16*x^6 +x^7 +16*x^8 +x^9)/(1 - x^10). (End)
%t PowerMod[Range[0, 100], 4, 20] (* _G. C. Greubel_, Apr 05 2016 *)
%o (Sage) [power_mod(n,4,20)for n in range(0, 87)] # _Zerinvary Lajos_, Oct 31 2009
%o (PARI) a(n)=n^4%20 \\ _Charles R Greathouse IV_, Apr 05 2016
%K nonn,easy
%O 0,3
%A _N. J. A. Sloane_, May 13 2002
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