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A102396
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A mod 2 related Jacobsthal sequence.
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2
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0, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 3, 1, 3, 3, 5, 1, 1, 1, 3, 1, 3, 3, 5, 1, 3, 3, 5, 3, 5, 5, 11, 1, 1, 1, 3, 1, 3, 3, 5, 1, 3, 3, 5, 3, 5, 5, 11, 1, 3, 3, 5, 3, 5, 5, 11, 3, 5, 5, 11, 5, 11, 11, 21, 1, 1, 1, 3, 1, 3, 3, 5, 1, 3, 3, 5, 3, 5, 5, 11, 1, 3, 3, 5, 3, 5, 5, 11, 3, 5, 5, 11, 5, 11, 11, 21, 1, 3
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OFFSET
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0,8
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COMMENTS
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Conjecture: all the terms are Jacobsthal numbers.
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LINKS
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FORMULA
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a(n) = Sum_{k=0..n} if(n+k == 1 (mod 3), C(n, k) mod 2, 0).
a(n) = Sum_{k=0..n} if(n+k == 2 (mod 3), C(n, k) mod 2, 0).
a(n) = (1/2) * Sum_{k=0..n} ({F(n+k)*binomial(n, k)} mod 2) where F = A000045.
Recurrence : a(0) = 0 then a(2n) = a(n) and a(2n+1) = 2*a(n) + 1 - 2*t(n) where t(n) = A010060(n) is the Thue-Morse sequence. - Benoit Cloitre, May 15 2005
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MATHEMATICA
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j[n_] := (2^n - (-1)^n) / 3; a[n_] := j[DigitCount[n, 2, 1]]; Array[a, 100, 0] (* Amiram Eldar, Jul 22 2023 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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