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 A005823 Numbers whose ternary expansion contains no 1's. (Formerly M1567) 49
 0, 2, 6, 8, 18, 20, 24, 26, 54, 56, 60, 62, 72, 74, 78, 80, 162, 164, 168, 170, 180, 182, 186, 188, 216, 218, 222, 224, 234, 236, 240, 242, 486, 488, 492, 494, 504, 506, 510, 512, 540, 542, 546, 548, 558, 560, 564, 566, 648, 650, 654, 656, 666, 668, 672, 674 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The set of real numbers between 0 and 1 that contain no 1's in their ternary expansion is the well-known Cantor set with Hausdorff dimension log 2 / log 3. Complement of A081606. - Reinhard Zumkeller, Mar 23 2003 Numbers n such that the n-th Apery number equals 1 (mod 3) (cf. A005258) - Benoit Cloitre, Nov 30 2003 Numbers n such that the n-th central Delannoy number equals 1 (mod 3) (cf. A001850) - Benoit Cloitre, Nov 30 2003 Numbers n such that there exists a permutation p_1, ..., p_n of 1, ..., n such that i + p_i is a power of 3 for every i - Ray Chandler, Aug 03 2004 Subsequence of A125292; A125291(a(n)) = 1 for n>0. - Reinhard Zumkeller, Nov 26 2006 A062756(a(n)) = 0. - Reinhard Zumkeller, Mar 02 2008 The first 2^n terms of the sequence could be obtained using the Cantor process for the segment [0,3^n-1]. E.g. for n=2 we have [0,{1},2,{3,4,5},6,{7},8]. The numbers outside of braces are the first 4 terms of the sequence. Therefore the terms of the sequence could be called "Cantor's numbers". - Vladimir Shevelev, Jun 13 2008 Mahler proved that positive a(n) is never a square. - Michel Marcus, Nov 12 2012 Define t: Z -> P(R) so that t(n) is the translated Cantor ternary set spanning [n, n+1], and let T be the union of t(a(n)) for all n. T = T * 3 = T / 3 is the closure of the Cantor ternary set under multiplication by 3. - Peter Munn, Oct 30 2019 REFERENCES K. J. Falconer, The Geometry of Fractal Sets, Cambridge, 1985; p. 14. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS T. D. Noe, Table of n, a(n) for n = 1..1024 J.-P. Allouche and J. Shallit, The ring of k-regular sequences, Theoretical Computer Sci., 98 (1992), 163-197. J.-P. Allouche and J. Shallit, The ring of k-regular sequences, Theoretical Computer Sci., 98 (1992), 163-197. Sajed Haque, Chapter 3.4 of Discriminators of Integer Sequences, 2017, See p. 45. Sajed Haque, Jeffrey Shallit, Discriminators and k-Regular Sequences, arXiv:1605.00092 [cs.DM], 2016. C. Kimberling, Affinely recursive sets and orderings of languages, Discrete Math., 274 (2004), 147-160. K. Mahler, The representation of squares to the base 3, Acta Arith. Vol. 53, Issue 1 (1989), 99-106. M. Mendes France and A. J. van der Poorten, From geometry to Euler identities, Theoret. Comput. Sci., 65 (1989), 213-220. Eric Weisstein's World of Mathematics, Cantor Set FORMULA a(n) = 2 * A005836(n). a(2n) = 3*a(n)+2, a(2n+1) = 3*a(n+1), a(1) = 0. a(n) = Sum_{k = 1..n} 1 + 3^A007814(k). - Philippe Deléham, Jul 09 2005 If the offset were changed to zero, then: a(0)=0, a(n+1)=f(a(n)+1,f(a(n)+1) where f(x,y) = if x<3 and x<>1 then y else if x mod 3 = 1 then f(y+1,y+1) else f(floor(x/3),y). - Reinhard Zumkeller, Mar 02 2008 G.f. g(x) satisfies g(x) = 3*g(x^2)*(1+1/x) + 2*x^2/(1-x^2). - Robert Israel, Jan 04 2015 MAPLE a:= proc(n) option remember;       `if`(n=1, 0, `if`(irem (n, 2, 'q')=0, 3*a(q)+2, 3*a(q+1)))     end: seq(a(n), n=1..100); # Alois P. Heinz, Apr 19 2012 MATHEMATICA Select[ Range[ 0, 729 ], (Count[ IntegerDigits[ #, 3 ], 1 ]==0)& ] Select[Range[0, 700], DigitCount[#, 3, 1]==0&] (* Harvey P. Dale, Mar 12 2016 *) PROG (PARI) is(n)=while(n, if(n%3==1, return(0), n\=3)); 1 \\ Charles R Greathouse IV, Apr 20 2012 (PARI) a(n)=n=binary(n-1); sum(i=1, #n, 2*n[i]*3^(#n-i)) \\ Charles R Greathouse IV, Apr 20 2012 (PARI) a(n)=2*fromdigits(binary(n-1), 3) \\ Charles R Greathouse IV, Aug 24 2016 (Python) def A005823(n):      return 2*int(format(n-1, 'b'), 3) # Chai Wah Wu, Jan 04 2015 CROSSREFS Twice A005836. Cf. A032924, A014263, A007089, A062756, A061392, A001196, A097252-A097262. Cf. A088917 (characteristic function), A306556. Sequence in context: A325686 A053355 A233572 * A259026 A178758 A024431 Adjacent sequences:  A005820 A005821 A005822 * A005824 A005825 A005826 KEYWORD nonn,easy,nice,look,base AUTHOR EXTENSIONS More terms from Sascha Kurz, Mar 24 2002 Offset corrected by N. J. A. Sloane, Mar 02 2008. This may require some of the formulas to be adjusted. STATUS approved

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Last modified October 1 00:54 EDT 2020. Contains 337440 sequences. (Running on oeis4.)