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 A153000 Toothpick sequence in the first quadrant. 31
 0, 1, 2, 3, 5, 8, 10, 11, 13, 16, 19, 23, 30, 38, 42, 43, 45, 48, 51, 55, 62, 70, 75, 79, 86, 95, 105, 120, 142, 162, 170, 171, 173, 176, 179, 183, 190, 198, 203, 207, 214, 223, 233, 248, 270, 290, 299, 303, 310, 319, 329, 344, 366, 387 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS From Omar E. Pol, Nov 29 2009: (Start) At stage 0, we start from a horizontal half toothpick at [(0,1),(1,1)]. This half toothpick represents one of the two components of the second toothpick placed in the toothpick structure of A139250. Consider only the toothpicks of length 2, so a(0) = 0. At stage 1 we place an orthogonal toothpick of length 2 centered at the end, so a(1) = 1. In each subsequent stage, for every exposed toothpick end, place an orthogonal toothpick centered at that end. The sequence gives the number of toothpicks after n stages. Note that this sequence contains even numbers and odd numbers, the same as A152978 (the first differences) which gives the number of toothpicks added at n-th stage. For more information see A139250. (End) A079559 gives the parity of this sequence, if n >= 1. - Omar E. Pol, Aug 13 2013 REFERENCES D. 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 LINKS Table of n, a(n) for n=0..53. 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. [There is a typo in Theorem 6: (13) should read u(n) = 4.3^(wt(n-1)-1) for n >= 2.], which is also available at arXiv:1004.3036v2, [math.CO], 2010. Omar E. Pol, Illustration of initial terms [From Omar E. Pol, Nov 29 2009] N. J. A. Sloane, Catalog of Toothpick and Cellular Automata Sequences in the OEIS Index entries for sequences related to toothpick sequences Index entries for sequences related to cellular automata FORMULA a(n) = (A139250(n+2)-3)/4 = (A152998(n+1)-1)/2. G.f.: (1+x)*(Product_{k>=1} (1+x^(2^k-1)+2*x^(2^k))-1)/((1-x)*(1+2*x)). - N. J. A. Sloane, May 20 2009 Contribution from Omar E. Pol, Oct 01 2011: (Start) a(n) = A152998(n+1) + A153003(n+1) - A139250(n+2) + 1. a(n) = A139250(n+2) - A153003(n+1) - 2. a(n) = A153003(n+1) - A152998(n+1). (End) a(n) = (A187220(n+3) - 7)/8. - Omar E. Pol, Feb 16 2013 MAPLE G := (1+x)*(mul(1+x^(2^k-1)+2*x^(2^k), k=1..20)-1)/((1-x)*(1+2*x)); # N. J. A. Sloane, May 20 2009 PROG (Python) def msb(n): t=0 while n>>t>0: t+=1 return 2**(t - 1) def a139250(n): k=(2*msb(n)**2 + 1)//3 return 0 if n==0 else k if n==msb(n) else k + 2*a139250(n - msb(n)) + a139250(n - msb(n) + 1) - 1 def a(n): return 0 if n==0 else (a139250(n + 2) - 3)//4 print([a(n) for n in range(101)]) # Indranil Ghosh, Jul 01 2017 CROSSREFS Cf. A139250, A139251, A152978, A153006. Cf. A152998, A160406. - Omar E. Pol, Nov 29 2009 Sequence in context: A189143 A047605 A295085 * A222172 A326379 A099107 Adjacent sequences: A152997 A152998 A152999 * A153001 A153002 A153003 KEYWORD nonn AUTHOR Omar E. Pol, Dec 16 2008, Dec 20 2008, Jan 02 2009 STATUS approved

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Last modified February 21 04:30 EST 2024. Contains 370219 sequences. (Running on oeis4.)