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Search: id:A125869
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| A125869 |
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Numbers n such that p=10n+1 is prime and cos(2pi/p) is an algebraic number of a 5-smooth degree, but not 3-smooth. |
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| 1, 3, 4, 6, 10, 15, 18, 24, 25, 27, 40, 54, 60, 64, 75, 81, 120, 160, 162, 180, 216, 225, 300, 400, 405, 480, 486, 648, 768, 810, 864, 900, 960, 972, 1125, 1440, 1536, 1600, 1944, 2160, 2187, 2250, 2304, 2400, 2560, 3240, 3375, 3645, 3750, 4096, 4320
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Numbers n such that p=10n+1 is prime and the greatest prime divisor of p-1 is 5.
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MATHEMATICA
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Do[If[Take[FactorInteger[EulerPhi[10n+1]][[ -1]], 1]=={5} && PrimeQ[10n+1], Print[n]], {n, 1, 10000}]
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CROSSREFS
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Cf. A024912, A125866-A125878.
Sequence in context: A074321 A167410 A085378 this_sequence A059618 A114736 A099417
Adjacent sequences: A125866 A125867 A125868 this_sequence A125870 A125871 A125872
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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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