OFFSET
1,1
COMMENTS
The prime number 2 in the definition is used because 2 is the only prime p such that p*q^k - 1 can be prime for more than one prime q.
a(9) > 3*10^13. - Tyler Busby, Jan 14 2023
MATHEMATICA
a[1]=2; a[n_]:=a[n]=(For[m=PrimePi[a[n-1]], Union[Table[PrimeQ[2 Prime[m]^k-1], {k, n}]]!={True}, m++]; Prime[m])]
PROG
(PARI) a(n)=forprime(m=2, , for(k=1, n, if(!ispseudoprime(2*m^k-1), next(2))); return(m)) \\ Charles R Greathouse IV, Oct 01 2013
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Farideh Firoozbakht, Sep 27 2013
EXTENSIONS
a(7) from Giovanni Resta, Oct 01 2013
a(8) from Tyler Busby, Jan 06 2023
STATUS
approved