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A117820
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Numbers such that UnitaryPhi(2*UnitaryPhi(n))=n.
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1
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1, 3, 15, 216, 255, 1080, 1728, 8640, 18360, 19344, 65535, 146880, 182880, 309504
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Odd terms are of the form Product_{0<=i<=m} F_i, 0<=m<=4, where F_i is a Fermat prime 2^(2^i)+1.
Contains also 1226400, 3456000, 14738400, 174182400, and 4294967295.
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EXAMPLE
| a(11)=3*5*17*257
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CROSSREFS
| Cf. A047994.
Sequence in context: A003505 A120601 A145272 * A126453 A007081 A126455
Adjacent sequences: A117817 A117818 A117819 * A117821 A117822 A117823
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KEYWORD
| nonn
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AUTHOR
| Yasutoshi Kohmoto (zbi74583(AT)boat.zero.ad.jp), Apr 30 2006
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