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Old 2021-06-08, 07:20   #1
Alfred
 
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May 2013
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Default 10^n+7: four PRPs

I've found four probable primes in the range 200001 <= n <= 500000:

Code:
n = 221628, 350071, 371696, 487291.
IMO any other 10^n+7 is composite.

The attached file should "prove" this assertion.
Attached Files
File Type: 7z 10w7.PRPsearch.Proof.txt.7z (1.16 MB, 15 views)
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Old 2021-06-08, 09:33   #2
axn
 
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Quote:
Originally Posted by Alfred View Post
IMO any other 10^n+7 is composite.
Do you mean "any other" in the specified range? Or n=[1..oo]?
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Old 2021-06-08, 11:23   #3
Alfred
 
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Any other in the specified range is meant.
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Old 2021-06-08, 11:48   #4
Dr Sardonicus
 
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Quote:
Originally Posted by axn View Post
Do you mean "any other" in the specified range? Or n=[1..oo]?
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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