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 A132868 #22 Mar 19 2025 20:30:46
%S A132868 1,3,7,20,60,182,547,1641,4921,14762,44286,132860,398581,1195743,
%T A132868 3587227,10761680,32285040,96855122,290565367,871696101,2615088301,
%U A132868 7845264902,23535794706,70607384120,211822152361,635466457083,1906399371247,5719198113740
%N A132868 a(n) = 3*a(n-1) - a(n-3) + 3*a(n-4), with initial values 1,3,7,20.
%H A132868 Andrew Howroyd, <a href="/A132868/b132868.txt">Table of n, a(n) for n = 0..1000</a>
%H A132868 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,0,-1,3).
%F A132868 4*a(n) = 3^(n+1) + A132951(n).
%F A132868 O.g.f.: (-1+2*x^2)/((3*x-1)*(x+1)*(x^2-x+1)) = -(3/4)/(3*x-1)-(1/12)/(x+1)+(1/3)*(x+1)/(x^2-x+1). - _R. J. Mathar_, Nov 28 2007
%F A132868 a(n) = (1/12)*(3^(n+2) - 4*cos((n+1)*Pi/3) + cos((n+1)*Pi) + 4*sqrt(3) * sin(((n+1)*Pi)/3) + I*sin((n+1)*Pi)). - _Harvey P. Dale_, Jan 21 2012
%F A132868 12*a(n) = -(-1)^n +3^(n+2) +4*A057079(n). - _R. J. Mathar_, Oct 03 2021
%t A132868 LinearRecurrence[{3,0,-1,3},{1,3,7,20},50] (* _Harvey P. Dale_, Jan 21 2012 *)
%Y A132868 Cf. A129339, A132951.
%K A132868 nonn,easy
%O A132868 0,2
%A A132868 _Paul Curtz_, Nov 22 2007