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Search: id:A069068
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| A069068 |
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Composite n+1 such that n*phi(n+1) is a perfect square. |
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+0
1
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| 9, 27, 50, 169, 242, 245, 945, 1127, 1280, 1352, 1694, 2430, 4335, 4410, 4624, 4802, 7500, 7935, 8624, 11913, 12544, 13254, 15050, 16384, 24642, 27869, 29403, 31827, 33489, 36750, 39675, 47045, 52800, 53290, 55470, 58806
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Trivially if n+1 is prime n*phi(n+1)=n^2. If n>1 n*phi(n) is never a perfect square.
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MATHEMATICA
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Select[Range[60000], !PrimeQ[ #+1] && IntegerQ[Sqrt[ # EulerPhi[1+# ]]]&] - T. D. Noe (noe(AT)sspectra.com), Nov 01 2006
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CROSSREFS
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Sequence in context: A133636 A020208 A020306 this_sequence A051412 A027468 A112524
Adjacent sequences: A069065 A069066 A069067 this_sequence A069069 A069070 A069071
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KEYWORD
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easy,nonn
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AUTHOR
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Benoit Cloitre (benoit7848c(AT)orange.fr), Apr 05 2002
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EXTENSIONS
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Corrected by T. D. Noe (noe(AT)sspectra.com), Nov 01 2006
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