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 A166147 a(n) = 4n^2 + 4n - 7. 6
 1, 17, 41, 73, 113, 161, 217, 281, 353, 433, 521, 617, 721, 833, 953, 1081, 1217, 1361, 1513, 1673, 1841, 2017, 2201, 2393, 2593, 2801, 3017, 3241, 3473, 3713, 3961, 4217, 4481, 4753, 5033, 5321, 5617, 5921, 6233, 6553, 6881, 7217, 7561, 7913, 8273, 8641 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Primes in the sequence are in A028886. - Bruno Berselli, Mar 16 2012 The number of active (ON,black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 643", based on the 5-celled von Neumann neighborhood. - Robert Price, May 19 2016 REFERENCES S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 N. J. A. Sloane, On the Number of ON Cells in Cellular Automata, arXiv:1503.01168 [math.CO], 2015 Eric Weisstein's World of Mathematics, Elementary Cellular Automaton S. Wolfram, A New Kind of Science Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = a(n-1)+8*n with n>1, a(1)=1. From Vincenzo Librandi, Mar 15 2012: (Start) G.f.: x*(1+14*x-7*x^2)/(1-x)^3. a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). (End) E.g.f.: (-7 + 8*x + 4*x^2)*exp(x) + 7. - G. C. Greubel, Apr 26 2016 MATHEMATICA CoefficientList[Series[(1+14x-7x^2)/(1-x)^3, {x, 0, 50}], x] (* or *) LinearRecurrence[{3, -3, 1}, {1, 17, 41}, 50] (* Vincenzo Librandi, Mar 15 2012 *) Table[4 n^2 + 4 n - 7, {n, 46}] (* Michael De Vlieger, Apr 27 2016 *) PROG (PARI) a(n)=8*binomial(n+1, 2)-7 \\ Charles R Greathouse IV, Jan 11 2012 (MAGMA) I:=[1, 17, 41]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // Vincenzo Librandi, Mar 15 2012 CROSSREFS Sequence in context: A163185 A138005 A267421 * A028886 A146443 A110226 Adjacent sequences:  A166144 A166145 A166146 * A166148 A166149 A166150 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Oct 08 2009 EXTENSIONS New name from Charles R Greathouse IV, Jan 11 2012 based on Paolo P. Lava formula STATUS approved

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Last modified July 18 15:26 EDT 2019. Contains 325143 sequences. (Running on oeis4.)