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A292686
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Sierpinski-type iteration: start with a(0)=1, at each step, replace 0 with 000 and 1 with 101.
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3
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OFFSET
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0,2
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COMMENTS
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See A292687 for the decimal representation of a(n) viewed as a "binary number", i.e., as written in base 2.
The Sierpinski carpet (A153490) can be seen as 2-dimensional version of this 1-dimensional variant. The classical Sierpinski gasket triangle (Pascal's triangle mod 2) and "Rule 18" (or Rule 90, A070886) and "Rule 22" (A071029) have similar graphs.
The n-th term a(n) has 3^n digits, the middle third of which are all zero. The digits of a(n) are again the first and last 3^n digits of a(n+1), separated by 3^n zeros.
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LINKS
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FORMULA
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a(n+1) = convert(5*a(n), from base 8, to base 2).
a(n+1) = (100^(3^n)+1)*a(n).
a(n) = Product_{k=0 .. n-1} (100^(3^k)+1).
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EXAMPLE
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a(0) = 1 -> 101 = a(1);
a(1) = 101 -> concat(101,000,101) = 101000101 = a(2).
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MATHEMATICA
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PROG
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(PARI) a(n, a=1)=for(k=1, n, a=fromdigits(binary(a)*5, 8)); fromdigits(binary(a), 10) \\ Illustration of the first formula.
(PARI) A292686(n)=prod(k=0, n-1, 100^(3^k)+1)
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CROSSREFS
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Cf. A292687 for the decimal representation of a(n) viewed as a "binary number", i.e., as written in base 2.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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