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A368624
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a(n) = Sum_{k = 1..n} (-1)^(n+k) * gcd(2*k, n).
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0
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1, 0, 3, 4, 5, 0, 7, 16, 9, 0, 11, 20, 13, 0, 15, 48, 17, 0, 19, 36, 21, 0, 23, 80, 25, 0, 27, 52, 29, 0, 31, 128, 33, 0, 35, 84, 37, 0, 39, 144, 41, 0, 43, 84, 45, 0, 47, 240, 49, 0, 51, 100, 53, 0, 55, 208, 57, 0, 59, 180, 61, 0, 63, 320, 65, 0, 67, 132, 69, 0
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OFFSET
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1,3
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LINKS
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FORMULA
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a(2*n+1) = 2*n + 1; a(4*n+2) = 0; a(4*n) = 4*A344372(n) = 4*Sum_{k = 1..n} gcd(2*k, n).
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MAPLE
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seq(add((-1)^(n+k) * gcd(2*k, n), k = 1..n), n = 1..70)
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MATHEMATICA
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Table[Sum[(-1)^(n+k) GCD[2k, n], {k, n}], {n, 70}] (* Harvey P. Dale, Jun 16 2024 *)
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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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