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 A135446 #18 Jan 11 2025 23:45:46
%S A135446 -1,-1,3,10,19,33,62,125,255,514,1027,2049,4094,8189,16383,32770,
%T A135446 65539,131073,262142,524285,1048575,2097154,4194307,8388609,16777214,
%U A135446 33554429,67108863,134217730,268435459,536870913,1073741822,2147483645,4294967295,8589934594,17179869187
%N A135446 a(n) = 3*a(n-1) - 3*a(n-2) + 2*a(n-3), with a(0) = a(1) = -1 and a(2) = 3.
%C A135446 Sequence identical to its third differences.
%H A135446 G. C. Greubel, <a href="/A135446/b135446.txt">Table of n, a(n) for n = 0..1000</a>
%H A135446 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3, -3, 2).
%F A135446 a(n+1) - 2*a(n) = hexaperiodic 1, 5, 4, -1, -5, -4, A130815.
%F A135446 a(n) = 2^n - 2*cos((Pi*n)/3) - (4*sqrt(3)/3)*sin((Pi*n)/3). Or, a(n) = 2^n + [ -2; -3; -1; 2; 3; 1]. - _Richard Choulet_, Dec 31 2007
%F A135446 G.f.: (1+x)*(1-3*x) / ( (2*x-1)*(x^2-x+1) ). - _R. J. Mathar_, Nov 07 2015
%t A135446 a = {-1, -1, 3}; Do[AppendTo[a, 3*a[[ -1]] - 3*a[[ -2]] + 2*a[[ -3]]], {40}]; a (* _Stefan Steinerberger_, Dec 22 2007 *)
%t A135446 LinearRecurrence[{3, -3, 2},{-1, -1, 3},31] (* _Ray Chandler_, Sep 23 2015 *)
%K A135446 sign,easy
%O A135446 0,3
%A A135446 _Paul Curtz_, Dec 13 2007