OFFSET
1,1
COMMENTS
According to the conjecture in A236374, this sequence should have infinitely many terms.
The prime 2^(a(34)-1)*phi(a(34)) - 1 = 2^(38771)*12888 - 1 has 11676 decimal digits.
LINKS
Zhi-Wei Sun, Table of n, a(n) for n = 1..34
EXAMPLE
a(1) = 3 since neither 2^(1-1)*phi(1) - 1 = 0 nor 2^(2-1)*phi(2) - 1 = 1 is prime, but 2^(3-1)*phi(3) - 1 = 4*2 - 1 = 7 is prime.
MATHEMATICA
q[m_]:=PrimeQ[2^(m-1)*EulerPhi[m]-1]
n=0; Do[If[q[m], n=n+1; Print[n, " ", m]], {m, 1, 10000}]
PROG
(PARI) s=[]; for(m=1, 1000, if(isprime(2^(m-1)*eulerphi(m)-1), s=concat(s, m))); s \\ Colin Barker, Jan 24 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Zhi-Wei Sun, Jan 24 2014
STATUS
approved