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Number of odd terms in f^n, where f = 1/(x*y)+1/x+1/y+y+x/y+x+x*y.
2

%I #22 Jul 12 2017 05:29:53

%S 1,7,7,21,7,49,21,95,7,49,49,147,21,147,95,333,7,49,49,147,49,343,147,

%T 665,21,147,147,441,95,665,333,1319,7,49,49,147,49,343,147,665,49,343,

%U 343,1029,147,1029,665,2331,21,147,147,441,147,1029,441,1995,95,665,665,1995,333,2331,1319,4837

%N Number of odd terms in f^n, where f = 1/(x*y)+1/x+1/y+y+x/y+x+x*y.

%C This is the number of ON cells in a certain 2-D CA in which the neighborhood of a cell is defined by f, and in which a cell is ON iff there was an odd number of ON cells in the neighborhood at the previous generation.

%C This is the odd-rule cellular automaton defined by OddRule 357 (see Ekhad-Sloane-Zeilberger "Odd-Rule Cellular Automata on the Square Grid" link).

%H Alois P. Heinz, <a href="/A253071/b253071.txt">Table of n, a(n) for n = 0..8191</a>

%H Shalosh B. Ekhad, N. J. A. Sloane, and Doron Zeilberger, <a href="http://arxiv.org/abs/1503.01796">A Meta-Algorithm for Creating Fast Algorithms for Counting ON Cells in Odd-Rule Cellular Automata</a>, arXiv:1503.01796, 2015; see also the <a href="http://www.math.rutgers.edu/~zeilberg/mamarim/mamarimhtml/CAcount.html">Accompanying Maple Package</a>.

%H Shalosh B. Ekhad, N. J. A. Sloane, and Doron Zeilberger, <a href="http://arxiv.org/abs/1503.04249">Odd-Rule Cellular Automata on the Square Grid</a>, arXiv:1503.04249, 2015.

%H N. J. A. Sloane, On the No. of ON Cells in Cellular Automata, Video of talk in Doron Zeilberger's Experimental Math Seminar at Rutgers University, Feb. 05 2015: <a href="https://vimeo.com/119073818">Part 1</a>, <a href="https://vimeo.com/119073819">Part 2</a>

%H N. J. A. Sloane, <a href="http://arxiv.org/abs/1503.01168">On the Number of ON Cells in Cellular Automata</a>, arXiv:1503.01168, 2015

%H <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a>

%F This is the Run Length Transform of A253072.

%e Here is the neighborhood f:

%e [0, X, X]

%e [X, 0, X]

%e [X, X, X]

%e which contains a(1) = 7 ON cells.

%p C:=f->subs({x=1, y=1}, f);

%p # Find number of ON cells in CA for generations 0 thru M defined by rule

%p # that cell is ON iff number of ON cells in nbd at time n-1 was odd

%p # where nbd is defined by a polynomial or Laurent series f(x, y).

%p OddCA:=proc(f, M) global C; local n, a, i, f2, p;

%p f2:=simplify(expand(f)) mod 2;

%p a:=[]; p:=1;

%p for n from 0 to M do a:=[op(a), C(p)]; p:=expand(p*f2) mod 2; od:

%p lprint([seq(a[i], i=1..nops(a))]);

%p end;

%p f:=1/(x*y)+1/x+1/y+y+x/y+x+x*y;

%p OddCA(f, 130);

%t (* f = A253072 *) f[0]=1; f[1]=7; f[2]=21; f[3]=95; f[4]=333; f[5]=1319; f[n_] := f[n] = -8 f[n-5] + 44 f[n-4] - 24 f[n-3] - 5 f[n-2] + 6 f[n-1]; Table[Times @@ (f[Length[#]]&) /@ Select[Split[IntegerDigits[n, 2]], #[[1]] == 1&], {n, 0, 63}] (* _Jean-François Alcover_, Jul 12 2017 *)

%Y Other CA's that use the same rule but with different cell neighborhoods: A160239, A102376, A071053, A072272, A001316, A246034, A246035, A253064, A253065, A253066, A252069.

%Y Cf. A253072.

%K nonn

%O 0,2

%A _N. J. A. Sloane_ and _Doron Zeilberger_, Feb 23 2015