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Search: id:A078927
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| A078927 |
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Smallest s for which there are exactly n primitive Pythagorean triangles with perimeter 2s; i.e. smallest s such that A078926(s) = n. |
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+0
3
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| 6, 858, 7140, 158730, 771342, 3120180, 9699690, 31651620
(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.
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EXAMPLE
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a(2)=858; the primitive Pythagorean triangles with edge lengths (364, 627, 725) and (195, 748, 773) both have perimeter 2*858=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[s=1, True, s++, If[ct[2s]==n, Return[s]]]
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CROSSREFS
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a(n) = A078928(n)/2. Cf. A078926.
Sequence in context: A020542 A045480 A006114 this_sequence A064430 A137801 A076667
Adjacent sequences: A078924 A078925 A078926 this_sequence A078928 A078929 A078930
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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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