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A233775
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Number of vertices in the n-th row of the Sierpinski gasket (cf. A047999).
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4
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1, 2, 3, 4, 5, 4, 6, 8, 9, 4, 6, 8, 10, 8, 12, 16, 17, 4, 6, 8, 10, 8, 12, 16, 18, 8, 12, 16, 20, 16, 24, 32, 33, 4, 6, 8, 10, 8, 12, 16, 18, 8, 12, 16, 20, 16, 24, 32, 34, 8, 12, 16, 20, 16, 24, 32, 36, 16, 24, 32, 40, 32, 48, 64, 65, 4, 6, 8, 10, 8, 12
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OFFSET
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0,2
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COMMENTS
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Equivalently, this is the coordination sequence for the Sierpinski gasket with respect to the apex. - N. J. A. Sloane, Sep 19 2020
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LINKS
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FORMULA
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a(0)=1, a(n) = (2^t(n) + 1) * 2^(c(n) - 1) where t(n) = A007814(n) is the number of trailing zeros in the binary representation of n and c(n) = A000120(n) is the total number of ones in the binary representation of n. - Johan Falk, Jun 24 2020
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EXAMPLE
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Illustration of initial terms:
--------------------------------------------------------
--------------------------------------------------------
. * 0 1 1
. /T\
. *---* 1 2 3
. /T\ /T\
. *---*---* 2 3 6
. /T\ /T\
. *---* *---* 3 4 10
. /T\ /T\ /T\ /T\
. *---*---*---*---* 4 5 15
. /T\ /T\
. *---* *---* 5 4 19
.
After five stages the number of "black" triangles in the structure is A006046(5) = 11 and the number of "black" triangles in row 5 is A001316(5-1) = 2. The number of vertices in row 5 is equal to 4, so a(5) = 4.
Written as an irregular triangle the sequence begins:
1;
2;
3;
4,5;
4,6,8,9;
4,6,8,10,8,12,16,17;
4,6,8,10,8,12,16,18,8,12,16,20,16,24,32,33;
4,6,8,10,8,12,16,18,8,12,16,20,16,24,32,34,8,12,16,20,16, 24,32,36,16,24,32,40,32,48,64,65;
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MAPLE
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A000120 := n -> add(i, i=convert(n, base, 2)):
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PROG
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(PARI) print1("1, "); for(k=1, 70, print1((2^valuation(k, 2)+1) *2^(hammingweight(k)-1), ", ")) \\ Hugo Pfoertner, Jul 27 2020
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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