%I #13 Dec 21 2016 02:43:21
%S -1,3,15,47,127,319,767,1791,4095,9215,20479,45055,98303,212991,
%T 458751,983039,2097151,4456447,9437183,19922943,41943039,88080383,
%U 184549375,385875967,805306367,1677721599,3489660927,7247757311,15032385535
%N a(n) = (n-1)*2^n - 1.
%C Prime for n = 2, 4, 5, 11, 28, 35, no more < 100.
%H G. C. Greubel, <a href="/A163383/b163383.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (5, -8, 4).
%F a(n) = A000337(n) - 2.
%F From _R. J. Mathar_, Jul 26 2009: (Start)
%F a(n) = 5*a(n-1) - 8*a(n-2) + 4*a(n-3).
%F G.f.: x*(1-8*x+8*x^2)/((x-1)*(-1+2*x)^2). (End)
%e a(28) = ((2^(28))*(28 - 1)) - 1 = 7247757311.
%t LinearRecurrence[{5, -8, 4}, {-1, 3, 15}, 100] (* _G. C. Greubel_, Dec 20 2016 *)
%o (PARI) Vec(x*(1-8*x+8*x^2)/((x-1)*(-1+2*x)^2) + O(x^50)) \\ _G. C. Greubel_, Dec 20 2016
%Y Cf. A000337.
%K easy,sign
%O 1,2
%A _Jonathan Vos Post_, Jul 25 2009