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 A254006 a(0) = 1, a(n) = 3*a(n-2) if n mod 2 = 0, otherwise a(n) = 0. 4
 1, 0, 3, 0, 9, 0, 27, 0, 81, 0, 243, 0, 729, 0, 2187, 0, 6561, 0, 19683, 0, 59049, 0, 177147, 0, 531441, 0, 1594323, 0, 4782969, 0, 14348907, 0, 43046721, 0, 129140163, 0, 387420489, 0, 1162261467, 0, 3486784401, 0, 10460353203, 0, 31381059609, 0, 94143178827 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Inspired by the Lévy C-curve, and generated using different construction rules as shown in the links. The length of this variant Lévy C-curve is an integer in the real quadratic number field Q(sqrt(3)), namely L(n) = A(n) + B(n)*sqrt(3) with A(n) = a(n) and B(n) = a(n-1), with  a(0) = 1. See the construction rule and the illustration in the links. Powers of 3 interspersed with zeros. - Colin Barker, Jan 26 2015 LINKS Colin Barker, Table of n, a(n) for n = 0..1000 Kival Ngaokrajang, Illustration of construction rule and initial terms Index entries for linear recurrences with constant coefficients, signature (0,3). FORMULA a(n) = 3*a(n-2) if n mod 2 = 0, otherwise a(n) = 0, a(0) = 1. a(n) = (3^(n/2)*(1+(-1)^n))/2. - Colin Barker, Jan 26 2015 G.f.: -1 / (3*x^2-1). - Colin Barker, Jan 26 2015 MATHEMATICA nxt[{n_, a_, b_}]:={n+1, b, If[OddQ[n], 3a, 0]}; Transpose[NestList[nxt, {1, 1, 0}, 50]][[2]] (* or *) With[{nn=25}, Riffle[3^Range[0, nn], 0]] (* Harvey P. Dale, Nov 30 2015 *) PROG (PARI) { a=1; print1(a, ", "); for (n=1, 100,      if (Mod(n, 2)==0,          a=a*3;          print1(a, ", "),          print1(0, ", ")      ) ) } (PARI) Vec(-1/(3*x^2-1) + O(x^100)) \\ Colin Barker, Jan 26 2015 CROSSREFS Cf. A251732, A251733. Sequence in context: A164597 A167295 A079442 * A321329 A016645 A217764 Adjacent sequences:  A254003 A254004 A254005 * A254007 A254008 A254009 KEYWORD nonn,easy AUTHOR Kival Ngaokrajang, Jan 26 2015 STATUS approved

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Last modified August 15 02:47 EDT 2022. Contains 356122 sequences. (Running on oeis4.)