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Search: id:A078928
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| A078928 |
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Smallest p for which there are exactly n primitive Pythagorean triangles with perimeter p; i.e. smallest p such that A070109(p) = n. |
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+0
2
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| 12, 1716, 14280, 317460, 1542684, 6240360, 19399380, 63303240
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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A Pythagorean triangle is a right triangle whose edge lengths are all integers; such a triangle is 'primitive' if the lengths are relatively prime.
Least perimeter common to exactly n primitive Pythagorean triangles. - Lekraj Beedassy (blekraj(AT)yahoo.com), May 14 2004
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EXAMPLE
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a(2)=1716; the primitive Pythagorean triangles with edge lengths (364, 627, 725) and (195, 748, 773) both have perimeter 1716.
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MATHEMATICA
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oddpart[n_] := If[OddQ[n], n, oddpart[n/2]]; ct[p_] := Length[Select[Divisors[oddpart[p/2]], p/2<#^2<p&&GCD[ #, p/2/# ]==1&]]; a[n_] := For[per=2, True, per+=2, If[ct[per]==n, Return[per]]]
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CROSSREFS
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a(n) = 2*A078927(n). Cf. A070109.
Sequence in context: A015011 A034280 A009120 this_sequence A013717 A015485 A013479
Adjacent sequences: A078925 A078926 A078927 this_sequence A078929 A078930 A078931
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KEYWORD
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nonn,more
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AUTHOR
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Dean Hickerson (dean(AT)math.ucdavis.edu), Dec 15 2002
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EXTENSIONS
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a(8) from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 19 2002
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