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A069953 Composite n such that (n-1)*phi(n) is a perfect square. 2
10, 28, 51, 170, 243, 246, 946, 1128, 1281, 1353, 1695, 2431, 4336, 4411, 4625, 4803, 7501, 7936, 8625, 11914, 12545, 13255, 15051, 16385, 24643, 27870, 29404, 31828, 33490, 36751, 39676, 47046, 52801, 53291, 55471, 58807, 66249, 72076, 74061, 81676, 90775 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
If k>1 k*phi(k) is not a perfect square. Trivially, if p is prime (p-1)*phi(p) is a perfect square.
LINKS
MATHEMATICA
psQ[n_]:=CompositeQ[n]&&IntegerQ[Sqrt[(n-1)EulerPhi[n]]]; Select[ Range[ 100000], psQ] (* Harvey P. Dale, Nov 08 2017 *)
PROG
(PARI) for(n=2, 120000, if(frac(sqrt((n-1+isprime(n))*eulerphi(n)))==0, print1(n, ", ")))
CROSSREFS
Sequence in context: A088407 A267012 A273195 * A113746 A177720 A117464
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Apr 27 2002
STATUS
approved

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Last modified April 12 22:48 EDT 2024. Contains 371639 sequences. (Running on oeis4.)