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 A051156 #21 Mar 06 2020 00:16:18
%S A051156 5,73,1082401,4432676798593,1298708349570020393652962442872833,
%T A051156 91355004067076339167413824240109498970069278721,
%U A051156 7588608256743087977590500540116743445925584618982806531428980886590618779326218241
%N A051156 a(n) = (2^p^2 - 1)/(2^p - 1) where p is the n-th prime.
%C A051156 Note that a(n) = Phi(p,2^p) or a(n) = Phi(p^2,2), where Phi(m,x) is the m-th cyclotomic polynomial and p is the n-th prime. - _Thomas Ordowski_, Feb 18 2014
%F A051156 a(n) = A070526(prime(n)), a(n) = A019320(prime(n)^2). - _Thomas Ordowski_, Feb 18 2014
%t A051156 Table[Cyclotomic[Prime[n]^2, 2], {n, 7}] (* _Arkadiusz Wesolowski_, May 13 2012 *)
%t A051156 Table[(2^Prime[n]^2-1)/(2^Prime[n]-1),{n,10}] (* _Harvey P. Dale_, Apr 06 2019 *)
%Y A051156 Cf. A051154, A051155, A051157.
%K A051156 nonn,easy
%O A051156 1,1
%A A051156 _N. J. A. Sloane_