20210608, 07:20  #1 
May 2013
Germany
5·17 Posts 
10^n+7: four PRPs
I've found four probable primes in the range 200001 <= n <= 500000:
Code:
n = 221628, 350071, 371696, 487291. The attached file should "prove" this assertion. 
20210608, 09:33  #2 
Jun 2003
13·17·23 Posts 

20210608, 11:23  #3 
May 2013
Germany
5·17 Posts 
Any other in the specified range is meant.

20210608, 11:48  #4 
Feb 2017
Nowhere
4,673 Posts 
I see the OP has answered graciously.
I would have been tempted to answer "Yes." I point out If the attached file was supposed to prove that 10^n + 7 is composite for all other n, it would have been big news if it actually did that. (Especially since 10^n + 7 is prime for n = 1, 2, 4, 8, and 9). A proof that 10^n + 7 is composite for all n greater than 5000000 would also be big news. 
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