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A180647
Numbers n such that 5 + phi(n)^3 is prime. Phi is Euler's totient function.
0
3, 4, 6, 13, 21, 26, 28, 35, 36, 39, 42, 43, 45, 49, 52, 56, 65, 67, 70, 72, 78, 79, 84, 86, 87, 90, 98, 104, 105, 112, 116, 127, 130, 134, 139, 140, 141, 144, 156, 158, 159, 168, 174, 177, 180, 188, 193, 199, 210, 212, 221, 236, 249, 254, 277, 278, 282, 291, 299
OFFSET
1,1
COMMENTS
The sequence appears to be infinite, but I have no proof.
EXAMPLE
a(5) = 21 since 5 + phi(21)^3 = 5 + 12^3 = 1733 is prime.
MATHEMATICA
Select[Range[300], PrimeQ[5+EulerPhi[#]^3]&] (* Harvey P. Dale, Oct 13 2024 *)
CROSSREFS
Cf. A000010.
Sequence in context: A032712 A226792 A286292 * A318345 A357356 A143100
KEYWORD
nonn
AUTHOR
Carmine Suriano, Sep 14 2010
STATUS
approved