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 A015532 #29 Sep 08 2022 08:44:40
%S A015532 0,1,4,23,120,641,3404,18103,96240,511681,2720404,14463383,76896360,
%T A015532 408829121,2173591004,11556167863,61439808480,326652408961,
%U A015532 1736688295204,9233320043543,49090098240600,260993633267201,1387605220753004,7377376315882423
%N A015532 a(n) = 4*a(n-1) + 7*a(n-2).
%C A015532 Pisano period lengths: 1, 2, 8, 4, 4, 8, 3, 4, 24, 4, 110, 8, 168, 6, 8, 8, 288, 24, 18, 4, ... . - _R. J. Mathar_, Aug 10 2012
%H A015532 Vincenzo Librandi, <a href="/A015532/b015532.txt">Table of n, a(n) for n = 0..1000</a>
%H A015532 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,7).
%F A015532 From _R. J. Mathar_, Apr 29 2008: (Start)
%F A015532 O.g.f.: x/(1 - 4*x - 7*x^2).
%F A015532 a(n) = -7^n*(A^n - B^n)/(2*sqrt(11)) where A = -1/(2+sqrt(11)) and B = 1/(sqrt(11)-2). (End)
%t A015532 a[n_]:=(MatrixPower[{{1,2},{1,-5}},n].{{1},{1}})[[2,1]]; Table[Abs[a[n]],{n,-1,40}] (* _Vladimir Joseph Stephan Orlovsky_, Feb 19 2010 *)
%t A015532 LinearRecurrence[{4, 7}, {0, 1}, 30] (* _Vincenzo Librandi_, Nov 12 2012 *)
%o A015532 (Sage) [lucas_number1(n,4,-7) for n in range(0, 21)]# _Zerinvary Lajos_, Apr 23 2009
%o A015532 (Magma) [n le 2 select n-1 else 4*Self(n-1)+7*Self(n-2): n in [1..30] ]; // _Vincenzo Librandi_, Nov 12 2012
%o A015532 (PARI) x='x+O('x^30); concat([0], Vec(x/(1-4*x-7*x^2))) \\ _G. C. Greubel_, Jan 01 2018
%K A015532 nonn,easy
%O A015532 0,3
%A A015532 _Olivier Gérard_