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Search: id:A125872
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| A125872 |
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Odd numbers n such that cos(2pi/n) is an algebraic number of an 11-smooth degree, but not 7-smooth. |
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1
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| 23, 67, 69, 89, 115, 121, 161, 199, 201, 207, 253, 267, 299, 331, 335, 345, 353, 363, 391, 397, 437, 445, 463, 469, 483, 575, 597, 603, 605, 617, 621, 623, 661, 667, 713, 727, 737, 759, 801, 805, 847, 851, 871, 881, 897, 943, 979, 989, 991, 993, 995, 1005
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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A regular polygon of a(n) sides can be constructed if one also has an angle trisector, 5-sector, 7-sector and 11-sector.
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MATHEMATICA
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Do[If[Take[FactorInteger[EulerPhi[2n+1]][[ -1]], 1]=={11}, Print[2n+1]], {n, 1, 10000}]] (*Artur Jasinski*)
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CROSSREFS
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Cf. A125866-A125878.
Adjacent sequences: A125869 A125870 A125871 this_sequence A125873 A125874 A125875
Sequence in context: A089823 A001346 A051875 this_sequence A104945 A141849 A125873
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KEYWORD
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nonn
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AUTHOR
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Artur Jasinski (grafix(AT)csl.pl), Dec 13 2006
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EXTENSIONS
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Edited by Don Reble (djr(AT)nk.ca), Apr 24 2007
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