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%I #10 Sep 08 2021 21:14:35
%S 1,4,13,16,22,40,46,56,94,104,121,160,364,526,862,968,1093,1312,1514,
%T 3146,3194,3280,3742,4376,5368,7280,7702,8744,9841,28418,29524,40880,
%U 69022,75920,88573,106288,157394
%N Numbers k such that (3^ord(3, k) - 1)/k is prime, where ord(3, k) is the multiplicative order of 3 (mod k).
%C The corresponding primes are 2, 2, 2, 5, 11, 2, 3851, 13, 1001523179, 7, 2, 41, 2, 605199588591144003100881306574406851660288427740394885828171, ...
%e 46 is in the sequence since ord(3, 46) = 11 and (3^11 - 1)/46 = 3851 is prime.
%t aQ[n_] := PrimeQ[(3^MultiplicativeOrder[3, n] - 1)/n]; Select[ Range[10000], aQ ]
%o (PARI) isok(n) = (gcd(n,3) == 1) && isprime((3^znorder(Mod(3, n)) - 1)/n); \\ _Michel Marcus_, Dec 30 2017
%Y Cf. A050975, A053446.
%K nonn,more
%O 1,2
%A _Amiram Eldar_, Dec 29 2017
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