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 A111571 #23 Feb 07 2025 00:34:54
%S A111571 1,1,-2,-1,1,0,-3,-3,-2,-5,-11,-16,-23,-39,-66,-105,-167,-272,-443,
%T A111571 -715,-1154,-1869,-3027,-4896,-7919,-12815,-20738,-33553,-54287,
%U A111571 -87840,-142131,-229971,-372098,-602069,-974171,-1576240,-2550407,-4126647,-6677058,-10803705
%N A111571 a(n) = a(n-1) + a(n-3) + a(n-4), n >= 4, with initial terms 1,1,-2,-1.
%C A111571 See comment and FAMP code for A111569.
%C A111571 Floretion Algebra Multiplication Program, FAMP Code: 1jesseq[B+H] with B = - .25'i + .25'j - .25i' + .25j' + k' - .5'kk' - .25'ik' - .25'jk' - .25'ki' - .25'kj' - .5e and H = + .75'ii' + .75'jj' + .75'kk' + .75e
%H A111571 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,1,1).
%F A111571 G.f.: (-1+3*x^2)/((1+x^2)*(x^2+x-1)).
%t A111571 LinearRecurrence[{1,0,1,1},{1,1,-2,-1},40] (* or *) CoefficientList[ Series[ (-1+3*x^2)/((1+x^2)*(x^2+x-1)),{x,0,40}],x] (* _Harvey P. Dale_, Apr 23 2011 *)
%Y A111571 Cf. A001638, A111569, A111570, A111572, A111573, A007598, A000045.
%K A111571 easy,sign
%O A111571 0,3
%A A111571 _Creighton Dement_, Aug 10 2005
%E A111571 Name clarified by _Robert C. Lyons_, Feb 06 2025