login
A180643
Numbers n such that 1+phi(n)^2 is prime. Phi is the Euler totient function.
1
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
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
KEYWORD
nonn
AUTHOR
Carmine Suriano, Sep 14 2010
STATUS
approved