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 A140498 #20 Jul 12 2025 08:34:18
%S A140498 1,3,7,15,33,75,171,387,873,1971,4455,10071,22761,51435,116235,262683,
%T A140498 593649,1341603,3031911,6851871,15484689,34994187,79084107,178723827,
%U A140498 403901721,912786003,2062824327,4661820135,10535345433,23809048875,53806570731,121598601867
%N A140498 a(n) = 3*a(n-1)-3*a(n-2)+3*a(n-3) with a(0)=1, a(1)=3, a(2)=7.
%C A140498 Second differences of A137256.
%H A140498 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,3).
%F A140498 G.f.: (1+x^2)/(1-3*x+3*x^2-3*x^3). - _Colin Barker_, Mar 28 2012
%t A140498 LinearRecurrence[{3,-3,3},{1,3,7},32] (* or *) CoefficientList[Series[(1+x^2)/(1-3*x+3*x^2-3*x^3),{x,0,31}],x] (* _James C. McMahon_, Jul 11 2025 *)
%o A140498 (Magma) m:=32; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!((1+x^2)/(1-3*x+3*x^2-3*x^3))); // _Bruno Berselli_, Mar 28 2012
%Y A140498 Cf. A137256.
%K A140498 nonn,easy
%O A140498 0,2
%A A140498 _Paul Curtz_, Jun 29 2008
%E A140498 More terms from _Colin Barker_, Mar 28 2012