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 A070876 Binary expansion is 1xx100...0 where xx = 00 or 11. 4
 9, 15, 18, 30, 36, 60, 72, 120, 144, 240, 288, 480, 576, 960, 1152, 1920, 2304, 3840, 4608, 7680, 9216, 15360, 18432, 30720, 36864, 61440, 73728, 122880, 147456, 245760, 294912, 491520, 589824, 983040, 1179648, 1966080, 2359296, 3932160 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (0,2). FORMULA From Bruno Berselli, Mar 02 2011: (Start) G.f.: 3*(3+5*x)/(1-2*x^2). a(n) = 3*(4-(-1)^n)*2^((2*n+(-1)^n-1)/4). Therefore: a(n) = 9*2^(n/2) for n even, otherwise a(n) = 15*2^((n-1)/2). a(n) = 2*a(n-2) for n>1. (End) MATHEMATICA a = {}; Do[a = Append[a, FromDigits[ Join[{1, 0, 0, 1}, Table[0, {n}]], 2]]; a = Append[a, FromDigits[ Join[{1, 1, 1, 1}, Table[0, {n}]], 2]], {n, 0, 20}]; a CoefficientList[Series[3 (3 + 5 x) / (1 - 2 x^2), {x, 0, 40}], x] (* Vincenzo Librandi, Jun 19 2013 *) PROG (MAGMA) [n le 2 select 6*n+3 else 2*Self(n-2): n in [1..38]]; // Bruno Berselli, Mar 02 2011 (PARI) x='x+O('x^99); Vec(3*(3+5*x)/(1-2*x^2)) \\ Altug Alkan, Sep 20 2018 CROSSREFS Cf. A070875. Sequence in context: A207675 A118236 A230306 * A266419 A161163 A058211 Adjacent sequences:  A070873 A070874 A070875 * A070877 A070878 A070879 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, May 19 2002 EXTENSIONS More terms from Robert G. Wilson v, May 20 2002 STATUS approved

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Last modified April 19 10:39 EDT 2019. Contains 322255 sequences. (Running on oeis4.)