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A069068 Composite numbers k+1 such that k*phi(k+1) is a perfect square. 1
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, 66248, 72075, 74060, 81675, 90774, 90972 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Trivially if k+1 is prime k*phi(k+1) = k^2. If k>1 k*phi(k) is never a perfect square.
LINKS
MATHEMATICA
Select[Range[60000], !PrimeQ[ #+1] && IntegerQ[Sqrt[ # EulerPhi[1+# ]]]&] (* T. D. Noe, Nov 01 2006 *)
CROSSREFS
Sequence in context: A020208 A020306 A330680 * A051412 A027468 A158926
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Apr 05 2002
EXTENSIONS
Corrected by T. D. Noe, Nov 01 2006
More terms from Amiram Eldar, Apr 29 2022
STATUS
approved

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)