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Search: id:A039770
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| A039770 |
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Numbers n such that phi(n) is a perfect square. |
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+0
14
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| 1, 2, 5, 8, 10, 12, 17, 32, 34, 37, 40, 48, 57, 60, 63, 74, 76, 85, 101, 108, 114, 125, 126, 128, 136, 160, 170, 185, 192, 197, 202, 204, 219, 240, 250, 257, 273, 285, 292, 296, 304, 315, 364, 370, 380, 394, 401, 432, 438, 444, 451, 456, 468, 489, 504, 505
(list; graph; listen)
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OFFSET
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1,2
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REFERENCES
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D. M. Burton, Elementary Number Theory, Allyn and Bacon Inc., Boston MA, 1976, p. 141.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..10000
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FORMULA
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a(n) seems to be asymptotic to c*n^(3/2) with 1<c<1.3 - Benoit Cloitre (benoit7848c(AT)orange.fr), Sep 08 2002
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EXAMPLE
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phi(34)=16=4*4.
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MATHEMATICA
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Select[ Range[ 600 ], IntegerQ[ Sqrt[ EulerPhi[ # ] ] ]& ]
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PROGRAM
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(PARI) for(n=1, 120, if(issquare(eulerphi(n)), print(n)))
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CROSSREFS
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Cf. A000010, A007614. A062732 gives the squares.
Sequence in context: A078345 A080228 A121294 this_sequence A047618 A059551 A126281
Adjacent sequences: A039767 A039768 A039769 this_sequence A039771 A039772 A039773
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KEYWORD
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nonn,easy,nice
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AUTHOR
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Olivier Gerard (ogerard(AT)ext.jussieu.fr)
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