A296079 a(n) = 1 if 1+phi(n) is prime, 0 otherwise, where phi = A000010, Euler totient function.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0

Offset: 1

Author

Antti Karttunen, Dec 05 2017

Keywords

• nonn

Comments

Out of the first 65537 values, 26197 are 1's (indicating primes), and 39340 are 0's, indicating nonprimes.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..65537
• Index entries for characteristic functions

Crossrefs

Characteristic function of A039698.

Cf. A039689 (positions of zeros).

Cf. also A296077, A296078, A296080.

Programs

Mathematica

Table[If[PrimeQ[EulerPhi[n]+1],1,0],{n,120}] (* Harvey P. Dale, Apr 23 2020 *)

PARI

A296079(n) = isprime(1+eulerphi(n));

Formula

a(n) = A010051(A039649(n)) = A010051(1+A000010(n)).

For all n, a(n) >= A010051(n) and a(2n) >= A010051(n).