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%I #19 Apr 27 2021 02:15:47
%S 2,5,13,41,145,545,2113,8321,33025,131585,525313,2099201,8392705,
%T 33562625,134234113,536903681,2147549185,8590065665,34360000513,
%U 137439477761,549756862465,2199025352705,8796097216513,35184380477441,140737505132545,562949986975745,2251799880794113
%N a(0)=2; for n > 0, a(n) = 2^(2*n-1) + 2^n + 1.
%C A bisection of A257418. Apart from first term, same as A085601.
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (7,-14,8).
%F From _Chai Wah Wu_, Apr 26 2021: (Start)
%F a(n) = 7*a(n-1) - 14*a(n-2) + 8*a(n-3) for n > 3.
%F G.f.: (-4*x^3 - 6*x^2 + 9*x - 2)/((x - 1)*(2*x - 1)*(4*x - 1)). (End)
%Y Cf. A257418, A085601, A343176.
%K nonn,easy
%O 0,1
%A _N. J. A. Sloane_, Apr 26 2021
%E a(18)-a(26) from _Martin Ehrenstein_, Apr 26 2021
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