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 A103204 a(1) = 2, a(2) = 4; a(n) = 2*a(n-1) - 1. 6

%I

%S 2,4,7,13,25,49,97,193,385,769,1537,3073,6145,12289,24577,49153,98305,

%T 196609,393217,786433,1572865,3145729,6291457,12582913,25165825,

%U 50331649,100663297,201326593,402653185,805306369,1610612737,3221225473

%N a(1) = 2, a(2) = 4; a(n) = 2*a(n-1) - 1.

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2).

%F a(n) = A003945(n-1) + 1.

%F a(n) = 3*2^(n-2) + 1 for n>1. - _Ralf Stephan_, May 18 2007

%F a(n) = A004119(n-1), n>1. - _R. J. Mathar_, Jun 11 2010

%F G.f.: x*(2-2*x-x^2)/(1-3*x+2*x^2). a(n) = 3*a(n-1)-2*a(n-2), n>3. - _Colin Barker_, Jan 29 2012

%t a[1] = 2; a[2] = 4; a[n_] := a[n] = 2*a[n - 1] - 1; Table[a[n], {n, 1, 32}]

%t Join[{2},NestList[2#-1&,4,40]] (* or *) LinearRecurrence[{3,-2},{2,4,7},40] (* _Harvey P. Dale_, Dec 04 2018 *)

%o (PARI) Vec(x*(2-2*x-x^2)/(1-3*x+2*x^2) + O(x^50)) \\ _Michel Marcus_, Jan 29 2016

%Y Cf. A003945, A004119.

%K nonn,easy

%O 1,1

%A _Roger L. Bagula_, Mar 19 2005

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Last modified July 24 12:47 EDT 2021. Contains 346273 sequences. (Running on oeis4.)