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 A080041 #13 Mar 23 2024 08:05:25
%S A080041 1,2,7,20,55,152,415,1136,3103,8480,23167,63296,172927,472448,1290751,
%T A080041 3526400,9634303,26321408,71911423,196465664,536754175,1466439680,
%U A080041 4006387711,10945654784,29904084991,81699479552,223207129087
%N A080041 a(n) = floor((1+sqrt(3))^n).
%H A080041 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,3,-2,-2).
%F A080041 a(n) = A080040(n) - (1+(-1)^n)/2.
%F A080041 G.f.: (1+2t^3)/( (t-1)*(1+t)*(2*t^2+2*t-1)).
%t A080041 CoefficientList[Series[(1+2t^3)/(1-2t-3t^2+2t^3+2t^4), {t, 0, 30}], t]
%t A080041 Floor[(1+Sqrt[3])^Range[0,30]] (* _Harvey P. Dale_, Sep 14 2012 *)
%Y A080041 Cf. A080040.
%K A080041 easy,nonn
%O A080041 0,2
%A A080041 Mario Catalani (mario.catalani(AT)unito.it), Jan 21 2003