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 A111574 #20 Feb 07 2025 00:35:22
%S A111574 1,-1,2,3,3,4,9,15,22,35,59,96,153,247,402,651,1051,1700,2753,4455,
%T A111574 7206,11659,18867,30528,49393,79919,129314,209235,338547,547780,
%U A111574 886329,1434111,2320438,3754547,6074987,9829536,15904521,25734055,41638578,67372635
%N A111574 a(n) = a(n-1) + a(n-3) + a(n-4), n >= 4, with initial terms 1,-1,2,3.
%C A111574 See comment and FAMP code for A111569.
%C A111574 Floretion Algebra Multiplication Program, FAMP Code: -4baseiseq[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 A111574 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 1, 1).
%F A111574 G.f.: (-1+2*x-3*x^2)/((x^2+x-1)*(x^2+1)).
%t A111574 LinearRecurrence[{1,0,1,1},{1,-1,2,3},40] (* _Harvey P. Dale_, Jan 24 2017 *)
%Y A111574 Cf. A001638, A111569, A111570, A111571, A111572, A111573, A111575, A111576.
%K A111574 easy,sign
%O A111574 0,3
%A A111574 _Creighton Dement_, Aug 10 2005
%E A111574 Name clarified by _Robert C. Lyons_, Feb 06 2025