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A070081
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Middle side of integer triangles [A070080(n) <= a(n) <= A070082(n)], sorted by perimeter, sides lexicographically ordered.
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74
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1, 2, 2, 3, 2, 3, 4, 3, 3, 4, 3, 5, 4, 3, 4, 5, 4, 4, 6, 5, 4, 5, 4, 6, 5, 4, 5, 7, 6, 5, 6, 4, 5, 5, 7, 6, 5, 6, 5, 8, 7, 6, 7, 5, 6, 5, 6, 8, 7, 6, 7, 5, 6, 6, 9, 8, 7, 8, 6, 7, 5, 6, 7, 6, 9, 8, 7, 8, 6, 7, 6, 7, 10, 9, 8, 9, 7, 8, 6, 7, 8, 6, 7, 7, 10, 9, 8, 9, 7
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OFFSET
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1,2
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LINKS
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G. C. Greubel, Table of n, a(n) for the first 55 rows, flattened
Reinhard Zumkeller, Integer-sided triangles
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FORMULA
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a(n) = A070083(n) - A070080(n) - A070082(n).
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MATHEMATICA
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m = 55 (* max perimeter *);
sides[per_] := Select[Reverse /@ IntegerPartitions[per, {3}, Range[ Ceiling[per/2]]], #[[1]] < per/2 && #[[2]] < per/2 && #[[3]] < per/2&];
triangles = DeleteCases[Table[sides[per], {per, 3, m}], {}] // Flatten[#, 1]& // SortBy[Total[#] m^3 + #[[1]] m^2 + #[[2]] m + #[[1]]&];
triangles[[All, 2]] (* Jean-François Alcover, Jul 09 2017 *)
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CROSSREFS
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Cf. A046129, A055593, A069595, A069594, A069598.
Cf. A070080, A070082, A070083, A070084, A070085, A070086.
Sequence in context: A340716 A181948 A238943 * A071647 A034883 A338643
Adjacent sequences: A070078 A070079 A070080 * A070082 A070083 A070084
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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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