[seqfan] Concatenate 5 digits = prime

[Eric Angelini]

Hello SeqFans,

Jean-Marc Falcoz has computed this seq. :

1,2,3,7,19,31,91,373,931,1931,1933,7193,11931,19311,93119,311931,
913733,1373313,7331373,9311931,19311931,19311933,71931193,119311931,
193119311,931193119,3119311931,9137331373,9311931193,...

... where any concatenation of 5 consecutive digits is a prime.

We clearly have a(1) = 1
            and a(n) smallest integer > a(n-1) not leading to an
                     *immediate* contradiction

Is the seq infinite? 

---

The seq where any concatenation of 6 consecutive digits is a prime
stops immediately:

1,2,3,4,5,7
the only possibility being 1,2,3,4,5,7,1 -- but no 6-digit prime 
starts with 34571-

... stops immediately unless we drop the above *immediate* constraint
(but the resulting seq might be too heavy to compute with brute force
(trials and errors).

Best,
É.