[seqfan] Re: (3^n+1)/2 is prime, A171381

[T. D. Noe]

Because these primes have a form (3^2^n+1)/2 which is similar to Fermat
primes 2^2^n+1, I think we can expect only a finite number of primes*.  It
is quite likely that all primes of both kinds have been found.

* See, for instance, the heuristic argument in Hardy and Wright, An
Introduction to the Theory of Numbers, bottom of page 18 in the sixth
edition.

Tony