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A360827
Primes p, not safe primes, such that the smallest factor of (2^(p-1)-1) / 3 is equal to p.
0
443, 647, 1847, 2243, 2687, 2699, 6263, 6563, 7487, 7583, 8627, 8663, 9419, 9767, 10223, 11867, 12323, 13187, 13907, 14627, 14723, 14783, 17747, 17783, 19739, 20639, 20807, 21863, 22307, 23747, 24107, 24923, 25127, 26759, 27983, 29207, 29819, 30839, 31247, 32303, 34403, 34439
OFFSET
1,1
EXAMPLE
443 is the first term since p = 443 is the first term of A359387 that is not in A005385 (i.e., (443-1)/2 = 13*17 is not prime).
647 is the second term since p = 647 is the first term (> 443) of A359387 that is not in A005385 (i.e., (647-1)/2 = 17*19 is not prime).
MATHEMATICA
q[p_] := ! PrimeQ[(p - 1)/2] && AllTrue[Range[p], ! PrimeQ[#] || PowerMod[2, p - 1, 3*p*#] > 1 &]; Select[Prime[Range[4, 4000]], q] (* Amiram Eldar, Mar 01 2023 *)
PROG
(PARI) forprime(p=11, 40000, if(!isprime((p-1)/2), forprime(div=5, p-1, if(Mod(2, div)^(p-1)==1, next(2))); print1(p, ", ")))
CROSSREFS
Equals A359387 \ A005385.
Sequence in context: A171392 A105980 A031519 * A031699 A158321 A293978
KEYWORD
nonn
AUTHOR
Alain Rocchelli, Feb 22 2023
STATUS
approved