cp's OEIS Frontend

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

%I A296079 #17 Apr 23 2020 15:33:00
%S A296079 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,
%T A296079 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,
%U A296079 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
%N A296079 a(n) = 1 if 1+phi(n) is prime, 0 otherwise, where phi = A000010, Euler totient function.
%C A296079 Out of the first 65537 values, 26197 are 1's (indicating primes), and 39340 are 0's, indicating nonprimes.
%H A296079 Antti Karttunen, <a href="/A296079/b296079.txt">Table of n, a(n) for n = 1..65537</a>
%H A296079 <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>
%F A296079 a(n) = A010051(A039649(n)) = A010051(1+A000010(n)).
%F A296079 For all n, a(n) >= A010051(n) and a(2n) >= A010051(n).
%t A296079 Table[If[PrimeQ[EulerPhi[n]+1],1,0],{n,120}] (* _Harvey P. Dale_, Apr 23 2020 *)
%o A296079 (PARI) A296079(n) = isprime(1+eulerphi(n));
%Y A296079 Characteristic function of A039698.
%Y A296079 Cf. A039689 (positions of zeros).
%Y A296079 Cf. also A296077, A296078, A296080.
%K A296079 nonn
%O A296079 1,1
%A A296079 _Antti Karttunen_, Dec 05 2017