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A070091
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Number of isosceles integer triangles with perimeter n and relatively prime side lengths.
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4
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0, 0, 1, 0, 1, 0, 2, 1, 1, 1, 3, 1, 3, 1, 2, 2, 4, 2, 5, 2, 2, 2, 6, 2, 5, 3, 5, 3, 7, 2, 8, 4, 4, 4, 6, 3, 9, 4, 6, 4, 10, 4, 11, 5, 6, 5, 12, 4, 10, 5, 8, 6, 13, 4, 10, 6, 8, 7, 15, 4, 15, 7, 10, 8, 12, 6, 17, 8, 10, 6, 18, 6, 18, 9, 10, 9, 14, 6, 20, 8, 13
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OFFSET
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1,7
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COMMENTS
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a(n) = A051493(n) - A005044(n-6).
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LINKS
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Table of n, a(n) for n=1..81.
R. Zumkeller, Integer-sided triangles
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EXAMPLE
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For n=15 there are A005044(15)=7 integer triangles: [1,7,7], [2,6,7], [3,5,7], [3,6,6], [4,4,7], [4,5,6] and [5,5,5]: four are isosceles: [1<7=7], [3<6=6], [4=4<7] and [5=5=5], but GCD(3,6,6)>1 and GCD(5,5,5)>1, therefore a(15)=2.
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CROSSREFS
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Cf. A070080, A070081, A070082, A059169, A070099, A070107, A070084, A070116.
Sequence in context: A105540 A057043 A211095 * A091981 A060247 A060246
Adjacent sequences: A070088 A070089 A070090 * A070092 A070093 A070094
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KEYWORD
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nonn
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AUTHOR
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Reinhard Zumkeller, May 05 2002
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STATUS
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approved
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