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 A187893 #28 Apr 11 2024 10:11:08
%S A187893 1,4,4,7,10,16,25,40,64,103,166,268,433,700,1132,1831,2962,4792,7753,
%T A187893 12544,20296,32839,53134,85972,139105,225076,364180,589255,953434,
%U A187893 1542688,2496121,4038808,6534928,10573735,17108662,27682396,44791057,72473452,117264508
%N A187893 a(0)=1, a(1)=4, a(n) = a(n-1) + a(n-2) - 1.
%H A187893 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-1).
%F A187893 G.f.: -x*(-1-2*x+4*x^2) / ( (x-1)*(x^2+x-1) ). - _R. J. Mathar_, Mar 15 2011
%F A187893 a(n) = 1+3*|A039834(n)| = 1+3*A000045(n). - _R. J. Mathar_, Mar 15 2011
%t A187893 Join[{a=1,b=4},Table[c=a+b-1;a=b;b=c,{n,100}]]
%t A187893 LinearRecurrence[{2,0,-1},{1,4,4},40] (* _Harvey P. Dale_, Jun 06 2020 *)
%o A187893 (PARI) a(n)=3*fibonacci(n)+1 \\ _Charles R Greathouse IV_, Oct 29 2016
%Y A187893 Cf. A000045, A000071, A001611, A001612, A039834, A187890.
%K A187893 nonn,easy
%O A187893 0,2
%A A187893 _Vladimir Joseph Stephan Orlovsky_, Mar 15 2011