A180643 Numbers n such that 1+phi(n)^2 is prime. Phi is the Euler totient function.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 17, 18, 22, 25, 32, 33, 34, 35, 37, 39, 40, 41, 44, 45, 48, 50, 52, 55, 56, 57, 60, 63, 66, 67, 70, 72, 74, 75, 76, 78, 81, 82, 84, 87, 88, 90, 100, 108, 110, 114, 116, 121, 126, 127, 129, 131, 132, 134, 143, 147, 150, 151, 155

Offset

1,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..2800

Example

a(20)=34 since 1+phi(34)^2 = 1+16^2 = 257 is prime.

Maple

select(t -> isprime(numtheory:-phi(t)^2+1), [$1..1000]); # Robert Israel, Mar 11 2020

Mathematica

Select[Range[200], PrimeQ[1+EulerPhi[#]^2]&] (* Harvey P. Dale, Aug 13 2014 *)

Prog

(PARI) isok(n) = isprime(1 + eulerphi(n)^2) \\ Michel Marcus, Jul 18 2013

Crossrefs

Cf. A000010, A127435 (primes in this sequence).

Sequence in context: A096902 A246081 A117325 * A017905 A333598 A044962

Adjacent sequences: A180640 A180641 A180642 * A180644 A180645 A180646

Keyword

nonn

Author

Carmine Suriano, Sep 14 2010

Status

approved