This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A360827 #23 Jul 02 2023 02:24:04 %S A360827 443,647,1847,2243,2687,2699,6263,6563,7487,7583,8627,8663,9419,9767, %T A360827 10223,11867,12323,13187,13907,14627,14723,14783,17747,17783,19739, %U A360827 20639,20807,21863,22307,23747,24107,24923,25127,26759,27983,29207,29819,30839,31247,32303,34403,34439 %N A360827 Primes p, not safe primes, such that the smallest factor of (2^(p-1)-1) / 3 is equal to p. %e A360827 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). %e A360827 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). %t A360827 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 *) %o A360827 (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, ", "))) %Y A360827 Equals A359387 \ A005385. %K A360827 nonn %O A360827 1,1 %A A360827 _Alain Rocchelli_, Feb 22 2023