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 A066807 #22 Apr 26 2025 08:27:41
%S A066807 3,3,57,4971027,29850020237398251227313,
%T A066807 17503832475167772961878049926333027042428946479619,
%U A066807 58167804601757508792865761341330650726830745576152064464908846133090363
%N A066807 Integers of the form (2^k+1)/k.
%C A066807 The next term a(8) has 152 digits and a(9) has 217 digits. - _Harvey P. Dale_, Oct 20 2014
%H A066807 Amiram Eldar, <a href="/A066807/b066807.txt">Table of n, a(n) for n = 1..12</a>
%F A066807 a(n) == 0 (mod 3).
%t A066807 Select[Table[(2^n+1)/n,{n,300}],IntegerQ] (* _Harvey P. Dale_, Oct 20 2014 *)
%o A066807 (PARI) lista(nn) = {for (n=1, nn, if (type(v = (2^n+1)/n) == "t_INT", print1(v, ", ")););} \\ _Michel Marcus_, Nov 20 2013
%Y A066807 Cf. A006521.
%K A066807 nonn
%O A066807 1,1
%A A066807 _Benoit Cloitre_, Jan 19 2002