Problems & Puzzles: Puzzles

Puzzle 800. A nice numbers sequence.

Abhiram R. Devesh sent the following nice puzzle.

I would like to propose a special prime that is formed by concatenating odd numbers on the right of "1" and even numbers on the left of "1".
a) for n=3, the number generated is 213 (Not Prime)
b) for n=6, the number generated is 642135 (Not Prime)

c) The first prime is generated for n=121 (255 digit long)

Q. Can you find the next three primes?

Contributions came from Jeff Heleen and Vicente Felipe Izquierdo

Jeff wrote

"...a prime is found when n=121 (255 digits)..." [already reported by Abhiram, see above]


Vicente wrote:

For n<=4500 the other only solution I found is n=1399 with length 4489.


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