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 A337847 #13 Sep 26 2020 11:29:47 %S A337847 457,1297,6481,14401,26497,44101,47521,47881,165601,225457,446881, %T A337847 560737,576721,677041,1037857,1049941,1649341,1903981,1934137,2291041, %U A337847 3990601,4110121,4262161,4663297,4736341,5293081,5317057,5372929,6410497,6535681,6651361,8122501 %N A337847 Odd integers k such that 3^((k-1)/2) == 1 (mod k*(k-2)). %C A337847 Computed terms are prime. Is this a possible primality test or are there pseudo primes? Terms are of the form 12k+1. %t A337847 Select[Range[3, 10^6, 2], PowerMod[3, (# - 1)/2, #*(# - 2)] == 1 &] (* _Amiram Eldar_, Sep 26 2020 *) %o A337847 (PARI) is(n) = n%2 && n>=3 && Mod(3, n*(n-2))^((n-1)/2) == 1 %Y A337847 Cf. A081762, A337818. %K A337847 nonn %O A337847 1,1 %A A337847 _Benoit Cloitre_, Sep 26 2020 %E A337847 More terms from _Amiram Eldar_, Sep 26 2020