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 A133145 #38 Feb 27 2024 03:00:49
%S A133145 1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,
%T A133145 4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,1,2,4,8,
%U A133145 1,2,4,8,1,2,4,8,1,2,4,8
%N A133145 Period 4: repeat [1, 2, 4, 8].
%H A133145 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,1).
%F A133145 a(n) == 2*a(n-1) mod 15.
%F A133145 a(n) = 2^(n mod 4). - _Jaume Oliver Lafont_, Mar 27 2009
%F A133145 a(n) = A160700(A000079(n)). [_Reinhard Zumkeller_, Jun 10 2009]
%F A133145 a(n) = 2^n (mod 15). G.f.: (1+2*x)*(4*x^2+1)/ ((1-x)*(1+x)*(x^2+1)). [_R. J. Mathar_, Apr 13 2010]
%F A133145 From _Wesley Ivan Hurt_, Jul 09 2016: (Start)
%F A133145 a(n) = a(n-4) for n>3.
%F A133145 a(n) = (15-6*cos(n*Pi/2)-5*cos(n*Pi)-12*sin(n*Pi/2)-5*I*sin(n*Pi))/4. (End)
%p A133145 seq(op([1, 2, 4, 8]), n=0..50); # _Wesley Ivan Hurt_, Jul 09 2016
%t A133145 PadRight[{}, 100, {1, 2, 4, 8}] (* _Wesley Ivan Hurt_, Jul 09 2016 *)
%t A133145 Table[First@ IntegerDigits[2^n, 16], {n, 0, 120}] (* _Michael De Vlieger_, Jul 09 2016 *)
%o A133145 (PARI) a(n)=2^(n%4) \\ _Jaume Oliver Lafont_, Mar 27 2009
%o A133145 (Sage) [power_mod(2,n,15) for n in range(0,80)] # _Zerinvary Lajos_, Nov 03 2009
%o A133145 (Magma) &cat [[1, 2, 4, 8]^^30]; // _Wesley Ivan Hurt_, Jul 09 2016
%Y A133145 Cf. A069705. [_Jaume Oliver Lafont_, Mar 27 2009]
%Y A133145 Cf. A000079, A160700.
%K A133145 nonn,easy
%O A133145 0,2
%A A133145 _Paul Curtz_, Dec 16 2007