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 A266973 #87 Sep 08 2022 08:46:15 %S A266973 1,4,16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16, %T A266973 13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4, %U A266973 16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16,13,1,4,16 %N A266973 a(n) = 4^n mod 17. %C A266973 Period 4: repeat [1, 4, 16, 13]. %H A266973 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1). %F A266973 G.f.: (1+4*x+16*x^2+13*x^3)/(1-x^4). %F A266973 a(n) = a(n-4) for n>3. %F A266973 From _Wesley Ivan Hurt_, Jun 29 2016: (Start) %F A266973 a(n) = (34 - 3*(5 + 3*I)*I^(-n) - 3*(5 - 3*I)*I^n)/4 where I=sqrt(-1). %F A266973 a(n) = (17 - 15*cos(n*Pi/2) - 9*sin(n*Pi/2))/2. (End) %p A266973 A266973:=n->power(4,n) mod 17: seq(A266973(n), n=0..100); # _Wesley Ivan Hurt_, Jun 29 2016 %t A266973 PowerMod[4, Range[0, 100], 17] %o A266973 (Magma) [Modexp(4, n, 17): n in [0..100]]; %Y A266973 Cf. similar sequences of the type 4^n mod p, where p is a prime: A010685 (5), A153727 (7), A168429 (11), A168430 (13), this sequence (17), A187532 (19). %K A266973 nonn,easy %O A266973 0,2 %A A266973 _Vincenzo Librandi_, Apr 06 2016