Ed Pegg Jr wrote:

> 2^17 - 1 = 131071. Both 131 and 071 are prime, or 131~071,

> or 3~(2^17-1), since it splits at the third position.

>

> What is the largest known splitable prime?

I have not heard of searches for large splitable primes.

One way to search them is to concatenate known primes.

27918*10^10000+1 was found in 1999 by Yves Gallot.

58789 is the smallest prime which can be put in front and give a prime:

D:>pfgw -t -q"5878927918*10^10000+1"

PFGW Version 1.2.0 for Windows [FFT v23.8]

Primality testing 5878927918*10^10000+1 [N-1, Brillhart-Lehmer-Selfridge]

Running N-1 test using base 3

Calling Brillhart-Lehmer-Selfridge with factored part 69.83%

5878927918*10^10000+1 is prime! (26.4531s+0.0023s)

The form k*10^n+1 was chosen to make the concatenation easily provable.

PrimeForm/GW prp tested and APTreeSieve sieved.

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Jens Kruse Andersen