%I #18 Dec 18 2023 14:49:04
%S 0,1,8,6,1,20,6,7,8,15,13,8,6,13,14,15,1,20,15,13,20,0,1,8,6,1,20,6,7,
%T 8,15,13,8,6,13,14,15,1,20,15,13,20,0,1,8,6,1,20,6,7,8,15,13,8,6,13,
%U 14,15,1,20,15,13,20,0,1,8,6,1,20,6,7,8,15,13,8,6,13,14,15,1,20,15,13,20
%N a(n) = n^3 mod 21.
%H G. C. Greubel, <a href="/A070483/b070483.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1).
%F From _G. C. Greubel_, Mar 28 2016: (Start)
%F a(n) = a(n-21).
%F G.f.: (-x -8*x^2 -6*x^3 -x^4 -20*x^5 -6*x^6 -7*x^7 -8*x^8 -15*x^9 -13*x^10 -8*x^11 -6*x^12 -13*x^13 -14*x^14 -15*x^15 -x^16 -20*x^17 -15*x^18 -13*x^19 -20*x^20)/(-1 + x^21). (End)
%t PowerMod[Range[0, 90], 3, 21] (* _G. C. Greubel_, Mar 28 2016 *)
%o (Sage) [power_mod(n,3,21 )for n in range(0, 84)] # _Zerinvary Lajos_, Oct 29 2009
%o (Magma) [Modexp(n, 3, 21): n in [0..100]]; // _Vincenzo Librandi_, Mar 29 2016
%o (PARI) a(n)=n^3%21 \\ _Charles R Greathouse IV_, Apr 06 2016
%K nonn,easy
%O 0,3
%A _N. J. A. Sloane_, May 12 2002
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