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A070909
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Triangle read by rows giving successive states of cellular automaton generated by "Rule 28" and by "Rule 156".
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16
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1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0
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OFFSET
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0,1
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COMMENTS
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Row n has length n+1.
Eigensequence of the triangle = A038754 (i.e., 1, 1, 2, 3, 6, 9, 18, ...) shifts to the left with multiplication by triangle A070909.
Generalized (conditional) Riordan array with k-th column generated by x^k/(1-x) if k is even, x^k otherwise.
Double Riordan array (1/(1 - x); x*(1 - x), x/(1 - x)) as defined in Davenport et al. The inverse array is the double Riordan array (1 - x - x^2; x/(1 - x - x^2), x*(1 - x - x^2)).
In general, double Riordan arrays of the form (g(x); x/g(x), x*g(x)), where g(x) = 1 + g_1*x + g_2*x^2 + ..., form a group under matrix multiplication with the group law given by (g(x); x/g(x), x*g(x)) * (G(x); x/G(x), x*G(x)) = (h(x); x/h(x), x*h(x)), where h(x) = G(x) + (g(x) - 1)*(G(x) + G(-x))/2. The inverse array of (g(x); x/g(x), x*g(x)) equals (f(x); x/f(x), x*f(x)), where f(x) = (2 - (g(x) - g(-x)))/(g(x) + g(-x)). (End)
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REFERENCES
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S. Wolfram, A New Kind of Science, Wolfram Media, 2002; Chapter 3.
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LINKS
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D. E. Davenport, L. W. Shapiro and L. C. Woodson, The Double Riordan Group, The Electronic Journal of Combinatorics, 18(2) (2012).
Eric Weisstein's World of Mathematics, Rule 28
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EXAMPLE
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Triangle begins
1;
1, 1;
1, 0, 1;
1, 0, 1, 1;
1, 0, 1, 0, 1;
1, 0, 1, 0, 1, 1;
1, 0, 1, 0, 1, 0, 1;
1, 0, 1, 0, 1, 0, 1, 1;
1, 0, 1, 0, 1, 0, 1, 0, 1;
1, 0, 1, 0, 1, 0, 1, 0, 1, 1;
Production matrix begins
1, 1;
0, -1, 1;
0, -1, 1, 1;
0, 0, 0, -1, 1;
0, 0, 0, -1, 1, 1;
0, 0, 0, 0, 0, -1, 1;
0, 0, 0, 0, 0, -1, 1, 1;
0, 0, 0, 0, 0, 0, 0, -1, 1;
0, 0, 0, 0, 0, 0, 0, -1, 1, 1;
0, 0, 0, 0, 0, 0, 0, 0, 0, -1, 1; (End)
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MATHEMATICA
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rows = 14; ca = CellularAutomaton[28, {{1}, 0}, rows-1]; Flatten[Table[ca[[k, 1 ;; k]], {k, 1, rows}]] (* Jean-François Alcover, May 24 2012 *)
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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