[seqfan] An (in)finite set

Tomasz Ordowski tomaszordowski at gmail.com
Sun Jun 13 20:46:06 CEST 2021


Dear readers!

The odd numbers k for which (k-1)/2 is not prime
such that p-1 | k-1 or k-1 | p-1 for every prime p | 2^(k-1)-1
are {3, 9, 13, 17, 19, 31, 33, 37, 43, 65, 79, 115, 129, 187, 223, 367,
403, 535, 763, 835}.
There are no more terms below 2217 [Amiram Eldar]. Is this set finite and
complete?
The subset of primes {3, 13, 17, 19, 31, 37, 43, 79, 223, 367}. Same
question.
Cf. https://oeis.org/A334797 (see comments section).

Best regards,

Thomas Ordowski



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