This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A168399 #30 Aug 03 2025 06:52:51
%S A168399 1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,
%T A168399 3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,
%U A168399 9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9,1,3,9
%N A168399 a(n) = 3^n mod 13.
%C A168399 Equivalently: 3^(n+3*m) mod 13. - _G. C. Greubel_, Jul 20 2016
%H A168399 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,1).
%F A168399 From _R. J. Mathar_, Apr 13 2010: (Start)
%F A168399 a(n) = a(n-3).
%F A168399 G.f.: (1 + 3*x + 9*x^2)/ ((1-x)*(1+x+x^2)). (End)
%t A168399 Table[Mod[3^n,13], {n,0,50}] (* _G. C. Greubel_, Jul 20 2016 *)
%o A168399 (Sage) [power_mod(3, n, 13)for n in range(0, 93)] #
%o A168399 (PARI) a(n)=lift(Mod(3,13)^n) \\ _Charles R Greathouse IV_, Mar 22 2016
%o A168399 (Magma) [Modexp(3, n, 13): n in [0..110]]; // _Vincenzo Librandi_, Jul 21 2016
%K A168399 nonn,easy
%O A168399 0,2
%A A168399 _Zerinvary Lajos_, Nov 25 2009