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 A271007 First differences of number of active (ON,black) cells in n-th stage of growth of two-dimensional cellular automaton defined by "Rule 245", based on the 5-celled von Neumann neighborhood. 1
 7, -4, 40, -31, 99, -87, 183, -171, 303, -291, 455, -443, 639, -627, 855, -843, 1103, -1091, 1383, -1371, 1695, -1683, 2039, -2027, 2415, -2403, 2823, -2811, 3263, -3251, 3735, -3723, 4239, -4227, 4775, -4763, 5343, -5331, 5943, -5931, 6575, -6563, 7239 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Initialized with a single black (ON) cell at stage zero. REFERENCES S. Wolfram, A New Kind of Science, Wolfram Media, 2002; p. 170. LINKS Robert Price, Table of n, a(n) for n = 0..127 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 FORMULA Conjectures from Colin Barker, Mar 28 2016: (Start) a(n) = 6+9*(-1)^n+4*n+4*(-1)^n*n^2 for n>5. a(n) = 4*n^2+4*n+15 for n>5 and even. a(n) = -4*n^2+4*n-3 for n>5 and odd. a(n) = -a(n-1)+2*a(n-2)+2*a(n-3)-a(n-4)-a(n-5) for n>8. G.f.: (7+3*x+22*x^2+3*x^3+3*x^4-3*x^5-4*x^6-3*x^7+8*x^8-4*x^10) / ((1-x)^2*(1+x)^3). (End) MATHEMATICA CAStep[rule_, a_]:=Map[rule[[10-#]]&, ListConvolve[{{0, 2, 0}, {2, 1, 2}, {0, 2, 0}}, a, 2], {2}]; code=245; stages=128; rule=IntegerDigits[code, 2, 10]; g=2*stages+1; (* Maximum size of grid *) a=PadLeft[{{1}}, {g, g}, 0, Floor[{g, g}/2]]; (* Initial ON cell on grid *) ca=a; ca=Table[ca=CAStep[rule, ca], {n, 1, stages+1}]; PrependTo[ca, a]; (* Trim full grid to reflect growth by one cell at each stage *) k=(Length[ca[]]+1)/2; ca=Table[Table[Part[ca[[n]][[j]], Range[k+1-n, k-1+n]], {j, k+1-n, k-1+n}], {n, 1, k}]; on=Map[Function[Apply[Plus, Flatten[#1]]], ca] (* Count ON cells at each stage *) Table[on[[i+1]]-on[[i]], {i, 1, Length[on]-1}] (* Difference at each stage *) CROSSREFS Cf. A271004. Sequence in context: A270468 A270983 A278047 * A271053 A270629 A270680 Adjacent sequences:  A271004 A271005 A271006 * A271008 A271009 A271010 KEYWORD sign,easy AUTHOR Robert Price, Mar 28 2016 STATUS approved

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Last modified September 22 22:24 EDT 2020. Contains 337291 sequences. (Running on oeis4.)