A180647 Numbers n such that 5 + phi(n)^3 is prime. Phi is Euler's totient function.

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.

Links

Table of n, a(n) for n=1..59.

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

Adjacent sequences: A180644 A180645 A180646 * A180648 A180649 A180650

Keyword

nonn

Author

Carmine Suriano, Sep 14 2010

Status

approved