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

Author

Carmine Suriano, Sep 14 2010

Keywords

• nonn

Examples

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

Links

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

Crossrefs

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

Programs

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 *)

PARI

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