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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 (list; graph; refs; listen; history; text; internal format)
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.

CROSSREFS

Cf. A000010.

Sequence in context: A032712 A226792 A286292 * A318345 A143100 A327584

Adjacent sequences:  A180644 A180645 A180646 * A180648 A180649 A180650

KEYWORD

nonn

AUTHOR

Carmine Suriano, Sep 14 2010

STATUS

approved

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Last modified December 8 09:32 EST 2019. Contains 329862 sequences. (Running on oeis4.)