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 A337831 #16 Sep 26 2020 11:29:05 %S A337831 5,101,62501,1020101,3512501,12650501,22598021,31562501,365328101, %T A337831 789062501,11412000101,64014060101 %N A337831 Odd integers k such that 7^((k-1)/2) + 1 == 0 (mod k*(k-1)/2). %C A337831 Computed terms are prime. %t A337831 Select[Range[3, 10^7, 2], PowerMod[7, (# - 1)/2, (t = #*(# - 1)/2)] == t - 1 &] (* _Amiram Eldar_, Sep 24 2020 *) %Y A337831 Cf. A337818. %K A337831 nonn,more %O A337831 1,1 %A A337831 _Benoit Cloitre_, Sep 24 2020 %E A337831 a(9)-a(12) from _Amiram Eldar_, Sep 25 2020