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 A151723 Total number of ON states after n generations of cellular automaton based on hexagons. 40
 0, 1, 7, 13, 31, 37, 55, 85, 127, 133, 151, 181, 235, 289, 331, 409, 499, 505, 523, 553, 607, 661, 715, 817, 967, 1069, 1111, 1189, 1327, 1489, 1603, 1789, 1975, 1981, 1999, 2029, 2083, 2137, 2191, 2293, 2443, 2545, 2599, 2701, 2875, 3097, 3295 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Analog of A151725, but here we are working on the triangular lattice (or the A_2 lattice) where each hexagonal cell has six neighbors. A cell is turned ON if exactly one of its six neighbors is ON. An ON cell remains ON forever. We start with a single ON cell. It would be nice to find a recurrence for this sequence! Has a behavior similar to A182840 and possibly to A182632. - Omar E. Pol, Jan 15 2016 REFERENCES S. M. Ulam, On some mathematical problems connected with patterns of growth of figures, pp. 215-224 of R. E. Bellman, ed., Mathematical Problems in the Biological Sciences, Proc. Sympos. Applied Math., Vol. 14, Amer. Math. Soc., 1962 (see Example 6, page 224). LINKS N. J. A. Sloane, Table of n, a(n) for n = 0..4095 [First 1026 terms from David Applegate and N. J. A. Sloane] David Applegate, The movie version David Applegate and N. J. A. Sloane, Table of n, A151724(n), A151723(n) for n = 0..1025 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.] Bradley Klee, Log-periodic coloring, over the half-hexagon tiling. N. J. A. Sloane, Catalog of Toothpick and Cellular Automata Sequences in the OEIS N. J. A. Sloane, Exciting Number Sequences (video of talk), Mar 05 2021 FORMULA a(n) = 6*A169780(n) - 6*n + 1 (this is simply the definition of A169780). a(n) = 1 + 6*A169779(n-2), n >= 2. - Omar E. Pol, Mar 19 2015 It appears that a(n) = a(n-2) + 3*(A256537(n) - 1), n >= 3. - Omar E. Pol, Apr 04 2015 MATHEMATICA A151723 = 0; A151723[n_] := Total[CellularAutomaton[{10926, {2, {{2, 2, 0}, {2, 1, 2}, {0, 2, 2}}}, {1, 1}}, {{{1}}, 0}, {{{n - 1}}}], 2]; Array[A151723, 47, 0](* JungHwan Min, Sep 01 2016 *) A151723L[n_] := Prepend[Total[#, 2] & /@ CellularAutomaton[{10926, {2, {{2, 2, 0}, {2, 1, 2}, {0, 2, 2}}}, {1, 1}}, {{{1}}, 0}, n - 1], 0]; A151723L (* JungHwan Min, Sep 01 2016 *) CROSSREFS Cf. A147562, A151724, A151725, A161206, A161644, A169779, A169780, A170898, A170905, A182632, A182840, A256536, A256537. Sequence in context: A073473 A272407 A040084 * A046139 A023243 A335794 Adjacent sequences: A151720 A151721 A151722 * A151724 A151725 A151726 KEYWORD nonn AUTHOR David Applegate and N. J. A. Sloane, Jun 13 2009 EXTENSIONS Edited by N. J. A. Sloane, Jan 10 2010 STATUS approved

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