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A069068 Composite n+1 such that n*phi(n+1) is a perfect square. 0
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; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Trivially if n+1 is prime n*phi(n+1)=n^2. If n>1 n*phi(n) is never a perfect square.

LINKS

Table of n, a(n) for n=1..36.

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

Adjacent sequences:  A069065 A069066 A069067 * A069069 A069070 A069071

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Apr 05 2002

EXTENSIONS

Corrected by T. D. Noe, Nov 01 2006

STATUS

approved

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Last modified February 26 00:08 EST 2020. Contains 332270 sequences. (Running on oeis4.)