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%I #16 Mar 16 2023 12:24:03
%S 1,3,7,15,33,75,171,387,873,1971,4455,10071,22761,51435,116235,262683,
%T 593649,1341603,3031911,6851871,15484689,34994187,79084107,178723827,
%U 403901721,912786003,2062824327,4661820135,10535345433,23809048875,53806570731,121598601867
%N 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 Second differences of A137256.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,3).
%F G.f.: (1+x^2)/(1-3*x+3*x^2-3*x^3). - _Colin Barker_, Mar 28 2012
%o (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 Cf. A137256.
%K nonn,easy
%O 0,2
%A _Paul Curtz_, Jun 29 2008
%E More terms from _Colin Barker_, Mar 28 2012