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A020990
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a(n) = Sum_{k=0..n} (-1)^k*A020985(k).
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5
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1, 0, 1, 2, 3, 2, 1, 0, 1, 0, 1, 2, 1, 2, 3, 4, 5, 4, 5, 6, 7, 6, 5, 4, 3, 4, 3, 2, 3, 2, 1, 0, 1, 0, 1, 2, 3, 2, 1, 0, 1, 0, 1, 2, 1, 2, 3, 4, 3, 4, 3, 2, 1, 2, 3, 4, 5, 4, 5, 6, 5, 6, 7, 8, 9, 8, 9, 10, 11, 10, 9, 8, 9, 8, 9, 10, 9, 10, 11
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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0,4
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LINKS
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FORMULA
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Brillhart and Morton (1978) list many properties.
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PROG
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(Haskell)
a020990 n = a020990_list !! n
a020990_list = scanl1 (+) $ zipWith (*) a033999_list a020985_list
(PARI) a(n) = sum(k=0, n, (-1)^(k+hammingweight(bitand(k, k>>1)))); \\ Michel Marcus, Oct 07 2017
(Python)
def A020990(n): return sum(-1 if ((m&(m>>1)).bit_count()^m)&1 else 1 for m in range(n+1)) # Chai Wah Wu, Feb 11 2023
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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