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 A048883 a(n) = 3^wt(n), where wt(n) = A000120(n). 50
 1, 3, 3, 9, 3, 9, 9, 27, 3, 9, 9, 27, 9, 27, 27, 81, 3, 9, 9, 27, 9, 27, 27, 81, 9, 27, 27, 81, 27, 81, 81, 243, 3, 9, 9, 27, 9, 27, 27, 81, 9, 27, 27, 81, 27, 81, 81, 243, 9, 27, 27, 81, 27, 81, 81, 243, 27, 81, 81, 243, 81, 243, 243, 729, 3, 9, 9, 27, 9, 27, 27, 81, 9, 27, 27, 81, 27, 81 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Or, a(n)=number of 1's ("live" cells) at stage n of a 2-dimensional cellular automata evolving by the rule: 1 if NE+NW+S=1, else 0. This is the odd-rule cellular automaton defined by OddRule 013 (see Ekhad-Sloane-Zeilberger "Odd-Rule Cellular Automata on the Square Grid" link). - N. J. A. Sloane, Feb 25 2015 Or, start with S=[1]; replace S by [S, 3*S]; repeat ad infinitum. Fixed point of the morphism 1 -> 13, 3 -> 39, 9 -> 9(27), ... = 3^k -> 3^k 3^(k+1), ... starting from a(0) = 1; 1 -> 13 -> 1339 -> = 1339399(27) -> 1339399(27)399(27)9(27)(27)(81) -> ..., . - Robert G. Wilson v, Jan 24 2006 Equals row sums of triangle A166453 (the square of Sierpiński's gasket, A047999). - Gary W. Adamson, Oct 13 2009 First bisection of A169697=1,5,3,19,3,. a(2n+2)+a(2n+3)=12,12,36,=12*A147610 ? Distribution of terms (in A000244): A011782=1,A000079 for first array, A000079 for second. - Paul Curtz, Apr 20 2010 a(A000225(n)) = A000244(n) and a(m) != A000244(n) for m < A000225(n). - Reinhard Zumkeller, Nov 14 2011 This sequence pertains to phenotype Punnett square mathematics. Start with X=1. Each hybrid cross involves the equation X:3X. Therefore, the ratio in the first (mono) hybrid cross is X=1:3X=3(1) or 3; or 3:1. When you move up to the next hybridization level, replace the previous cross ratio with X. X now represents 2 numbers-1:3. Therefore, the ratio in the second (di) hybrid cross is X=(1:3):3X=[3(1):3(3)] or (3:9). Put it together and you get 1:3:3:9. Each time you move up a hybridization level, replace the previous ratio with X, and use the same equation-X:3X to get its ratio. - John Michael Feuk, Dec 10 2011 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 0..10000 David Applegate, The movie version David Applegate, Omar E. Pol and N. J. A. Sloane, The Toothpick Sequence and Other Sequences from Cellular Automata, Congressus Numerantium, Vol. 206 (2010), 157-191 Shalosh B. Ekhad, N. J. A. Sloane, and  Doron Zeilberger, A Meta-Algorithm for Creating Fast Algorithms for Counting ON Cells in Odd-Rule Cellular Automata, arXiv:1503.01796 [math.CO], 2015; see also the Accompanying Maple Package. Shalosh B. Ekhad, N. J. A. Sloane, and  Doron Zeilberger, Odd-Rule Cellular Automata on the Square Grid, arXiv:1503.04249 [math.CO], 2015. Tanya Khovanova, There are no coincidences, arXiv preprint 1410.2193 [math.CO], 2014. Tanya Khovanova and Joshua Xiong, Nim Fractals, arXiv:1405.594291 [math.CO] (2014), p. 10. T. Pisanski and T. W. Tucker, Growth in Repeated Truncations of Maps, Atti. Sem. Mat. Fis. Univ. Modena, Vol. 49 (2001), 167-176. (preprint) Omar E. Pol, Illustration of initial terms: Fig. 1. Neighbors of the vertices, Fig. 2. Overlapping squares, Fig. 3. One-step bishop, (Nov 06 2009) N. J. A. Sloane, On the No. of ON Cells in Cellular Automata, Video of talk in Doron Zeilberger's Experimental Math Seminar at Rutgers University, Feb. 05 2015: Part 1, Part 2 N. J. A. Sloane, Catalog of Toothpick and Cellular Automata Sequences in the OEIS N. J. A. Sloane, On the Number of ON Cells in Cellular Automata, arXiv:1503.01168 [math.CO], 2015. R. Stephan, Divide-and-conquer generating functions. I. Elementary sequences, arXiv:math/0307027 [math.CO], 2003. FORMULA a(n) = product{k=0..log_2(n), 3^b(n, k)}, b(n, k)=coefficient of 2^k in binary expansion of n(offset 0). - Paul D. Hanna a(n) = 3a(n/2) if n is even, else a(n)=a((n+1)/2). G.f.: Prod_{k>=0} (1+3*x^(2^k)). The generalization k^A000120 has generating function (1 + kx)(1 + kx^2)(1 + kx^4) ... a(n+1) = sum(i=0, n, {binomial(n, i) (mod 2)}*sum(j=0, i, {binomial(i, j) (mod 2)})). - Benoit Cloitre, Nov 16 2003 1) a(4n),a(4n+1),a(4n+2),a(4n+3)=a(n)*(period 4:repeat 1,3,3,9) ? ,a(0)=1. 2) a(n)=1,3*A147610(n). Note A147582=1,4,4,12,4,12,12,36,=1,4*A147610. - Paul Curtz, Apr 20 2010 a(0)=1, a(n) = 3*a(n-A053644(n)) for n>0. - Joe Slater, Jan 31 2016 EXAMPLE From Omar E. Pol, Jun 07 2009: (Start) Triangle begins: 1; 3; 3,9; 3,9,9,27; 3,9,9,27,9,27,27,81; 3,9,9,27,9,27,27,81,9,27,27,81,27,81,81,243; 3,9,9,27,9,27,27,81,9,27,27,81,27,81,81,243,9,27,27,81,27,81,81,243,27,... Or 1; 3,3; 9,3,9,9; 27,3,9,9,27,9,27,27; 81,3,9,9,27,9,27,27,81,9,27,27,81,27,81,81; 243,3,9,9,27,9,27,27,81,9,27,27,81,27,81,81,243,9,27,27,81,27,81,81,243,27... (End) MATHEMATICA Nest[ Join[#, 3#] &, {1}, 6] (* Robert G. Wilson v, Jan 24 2006 and modified Jul 27 2014*) a[n_] := 3^DigitCount[n, 2, 1]; Array[a, 80, 0] (* Jean-François Alcover, Nov 15 2017 *) PROG (PARI) a(n)=n=binary(n); 3^sum(i=1, #n, n[i]) (Haskell) a048883 = a000244 . a000120  -- Reinhard Zumkeller, Nov 14 2011 CROSSREFS For generating functions Prod_{k>=0} (1+a*x^(b^k)) for the following values of (a,b) see: (1,2) A000012 and A000027, (1,3) A039966 and A005836, (1,4) A151666 and A000695, (1,5) A151667 and A033042, (2,2) A001316, (2,3) A151668, (2,4) A151669, (2,5) A151670, (3,2) A048883, (3,3) A117940, (3,4) A151665, (3,5) A151671, (4,2) A102376, (4,3) A151672, (4,4) A151673, (4,5) A151674. A generalization of A001316. Cf. A102376. Partial sums give A130665. - David Applegate, Jun 11 2009 Cf. A000079, A122018, A166453. Sequence in context: A266533 A151710 A160121 * A241717 A217883 A036553 Adjacent sequences:  A048880 A048881 A048882 * A048884 A048885 A048886 KEYWORD nonn,nice,easy,hear AUTHOR EXTENSIONS Corrected by Ralf Stephan, Jun 19 2003 Entry revised by N. J. A. Sloane, May 30 2009 Offset changed to 0, Jun 11 2009 STATUS approved

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