[math-fun] 1, 2, 3.

Is apparently the complete sequence of solutions to PrimeQ[1+Hyperfactorial@x]. (Checked through a couple of hundred.) (Unconvincing) probabilistic arguments "predict" finiteness of prime subsequences of (sufficiently) rapidly growing sequences, but {1, 2, 3} seems a little too pat. Maybe RCS can conjure one of his magic case arguments. The complete list of prime 1+BarnesG seems to be 1, 2, 3, 4, 5, 9, 16. (Checked through 278.) —rwg