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A292077
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a(n) = 0 if n=1; a(n) = 1-a(n-2) if n is odd; a(n) = 1-a(n/2) if n is even.
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6
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0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0
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OFFSET
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1
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REFERENCES
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Dekking, Michel, Michel Mendes France, and Alf van der Poorten. "Folds." The Mathematical Intelligencer, 4.3 (1982): 130-138 & front cover, and 4:4 (1982): 173-181 (printed in two parts). See Section 1.5.
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LINKS
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FORMULA
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G.f.: Sum_{k>=0} (z^(2*4^k)/(1-z^(8*4^k)) + z^(3*4^k)/(1-z^(4*4^k))). (End)
Write n = (2*k+1) * 2^e, then a(n) = (k+e) mod 2.
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MAPLE
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f:= proc(n) local k, m;
k:= padic:-ordp(n, 2);
m:= n/2^k;
(1 + (-1)^((m+1)/2+k))/2
end proc:
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MATHEMATICA
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a[1] = 0; a[n_] := a[n] = 1 - If[OddQ[n], a[n-2], a[n/2]];
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PROG
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(PARI) a(n) = if (n==1, 0, if (n%2, 1 - a(n-2), 1 - a(n/2)));
(PARI) a(n) = my(e=valuation(n, 2), k=bittest(n, e+1)); (k+e)%2 \\ Jianing Song, Nov 27 2021
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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