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 A087965 #15 Jul 10 2024 02:58:12
%S A087965 2,4,16,36,120,256,456,1296,2556,2704,3816,3856,4356,5544,6480,8008,
%T A087965 9216,10440,10620,11952,16212,22896,23436,26320,26796,27840,28680,
%U A087965 35208,43056,44100,47520,47880,49680,51120,57240,61920,62568,63168,63936
%N A087965 Numbers k such that 2^k - 1 is divisible by (k-1).
%C A087965 Solutions to 2^x == 1 (mod x-1).
%H A087965 Amiram Eldar, <a href="/A087965/b087965.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..300 from Harvey P. Dale)
%t A087965 Join[{2},Select[Range[2,64000],PowerMod[2,#,#-1]==1&]] (* _Harvey P. Dale_, Jun 01 2021 *)
%o A087965 (PARI) is(k) = !(k % 2) && Mod(2, k-1)^k == 1; \\ _Amiram Eldar_, Jul 10 2024
%Y A087965 Cf. A006521.
%K A087965 nonn
%O A087965 1,1
%A A087965 _Labos Elemer_, Sep 22 2003