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A307828
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Number of integer-sided triangles with perimeter n whose smallest side-length divides n.
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3
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0, 0, 1, 0, 1, 1, 1, 1, 2, 1, 1, 3, 1, 1, 4, 3, 1, 3, 1, 5, 4, 1, 1, 8, 4, 1, 4, 6, 1, 8, 1, 7, 4, 1, 8, 12, 1, 1, 4, 14, 1, 9, 1, 8, 12, 1, 1, 18, 5, 8, 4, 9, 1, 10, 10, 17, 4, 1, 1, 28, 1, 1, 13, 15, 11, 11, 1, 11, 4, 18, 1, 31, 1, 1, 15, 12, 11, 12, 1, 32
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OFFSET
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1,9
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LINKS
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FORMULA
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a(n) = Sum_{k=1..floor(n/3)} Sum_{i=k..floor((n-k)/2)} sign(floor((i+k)/(n-i-k+1)) * (1 - ceiling(n/k) + floor(n/k)).
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MATHEMATICA
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Table[Sum[Sum[(1 - Ceiling[n/k] + Floor[n/k]) Sign[Floor[(i + k)/(n - i - k + 1)]], {i, k, Floor[(n - k)/2]}], {k, Floor[n/3]}], {n, 100}]
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PROG
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(PARI) A307828(n) = sum(k=1, floor(n/3), sum(i=k, floor((n-k)/2), sign(floor((i+k)/(n-i-k+1)) * (1 - ceil(n/k) + floor(n/k))))); \\ Antti Karttunen, Dec 05 2021
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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