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A106400
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Thue-Morse sequence: let A_k denote the first 2^k terms; then A_0 = 1 and for k >= 0, A_{k+1} = A_k B_k, where B_k is obtained from A_k by interchanging 1's and -1's.
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30
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1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1
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OFFSET
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0,1
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COMMENTS
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See A010060, the main entry for the Thue-Morse sequence, for additional information. - N. J. A. Sloane, Aug 13 2014
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LINKS
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FORMULA
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a(n) = (-1)^wt(n), where wt(n) is the binary weight of n, A000120(n).
G.f. A(x) satisfies 0 = f(A(x), A(x^2), A(x^4)) where f(u, v, w) = v^3 - 2*u*v*w + u^2*w.
G.f. A(x) satisfies 0 = f(A(x), A(x^2), A(x^3), A(x^6)) where f(u1, u2, u3, u6) = u6*u1^3 - 3*u6*u2*u1^2 + 3*u6*u2^2*u1 - u3*u2^3.
Euler transform of sequence b(n) where b(2^k) = -1 and zero otherwise.
G.f.: Product_{k>=0} (1 - x^(2^k)) = A(x) = (1-x) * A(x^2).
a(n) = B_n(-A038712(1)*0!, ..., -A038712(n)*(n-1)!)/n!, where B_n(x_1, ..., x_n) is the n-th complete Bell polynomial. See the Wikipedia link for complete Bell polynomials , and A036040 for the coefficients of these partition polynomials. - Gevorg Hmayakyan, Jul 10 2016 (edited by - Wolfdieter Lang, Aug 31 2016)
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EXAMPLE
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G.f. = 1 - x - x^2 + x^3 - x^4 + x^5 + x^6 - x^7 - x^8 + x^9 + x^10 + ...
The first 2^2 = 4 terms are 1, -1, -1, 1. Exchanging 1 and -1 gives -1, 1, 1, -1, which are a(4) through a(7). - Michael B. Porter, Jul 29 2016
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MAPLE
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subs("0"=1, "1"=-1, StringTools:-Explode(StringTools:-ThueMorse(1000))); # Robert Israel, Sep 01 2015
# third Maple program:
a:= n-> (-1)^add(i, i=Bits[Split](n)):
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MATHEMATICA
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tm[0] = 0; tm[n_?EvenQ] := tm[n/2]; tm[n_] := 1 - tm[(n-1)/2]; Table[(-1)^tm[n], {n, 0, 101}] (* Jean-François Alcover, Oct 24 2013 *)
Nest[ Flatten[# /. {1 -> {1, -1}, -1 -> {-1, 1}}] &, {1}, 7] (* Robert G. Wilson v, Apr 07 2014 *)
Table[Coefficient[Product[1 - x^(2^k), {k, 0, Log2[n + 1]}], x, n], {n, 0, 20}] (* Vladimir Reshetnikov, Nov 11 2016 *)
(-1)^ThueMorse[Range[0, 100]] (* Paolo Xausa, Dec 18 2023 *)
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PROG
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(PARI) {a(n) = if( n<1, n>=0, a(n\2) * (-1)^(n%2))};
(PARI) {a(n) = my(A, m); if( n<1, n==0, m=1; A = 1 + O(x); while( m<=n, m*=2; A = subst(A, x, x^2) * (1-x)); polcoeff(A, n))};
(PARI) a(n) = { 1 - 2 * (hammingweight(n) % 2) }; \\ Gheorghe Coserea, Aug 30 2015
(Haskell)
import Data.List (transpose)
a106400 n = a106400_list !! n
a106400_list = 1 : concat
(transpose [map negate a106400_list, tail a106400_list])
(Magma) [1-2*(&+Intseq(n, 2) mod(2)): n in [0..100]]; // Vincenzo Librandi, Sep 01 2015
(Python)
def aupto(nn):
A = [1]
while len(A) < nn+1: A += [-i for i in A]
return A[:nn+1]
(Python)
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CROSSREFS
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KEYWORD
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sign,easy
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AUTHOR
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STATUS
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approved
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