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 A291993 #9 Nov 11 2019 13:48:17
%S A291993 43,117307,2801,6568801,29078814248401,3421093417510114543,
%T A291993 79787519018560501,16148168401,1628413557556843,13564461457,
%U A291993 402488219476647465854701,13841169553,11898664849,655417289594537954307682339857743931943,33232924804801
%N A291993 Primes of the form Phi(k, -7), where Phi is the cyclotomic polynomial.
%H A291993 Robert Price, <a href="/A291993/b291993.txt">Table of n, a(n) for n = 1..23</a>
%H A291993 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/papers/cyclotomic.html">Cyclotomic polynomials and prime numbers</a>
%H A291993 <a href="/index/Cy#CyclotomicPolynomialsValuesAtX">Index entries for cyclotomic polynomials,values at X</a>
%t A291993 Select[Table[Cyclotomic[k,-7], {k, 0, 100}], PrimeQ[#] &]
%Y A291993 Cf. A138923.
%K A291993 nonn
%O A291993 1,1
%A A291993 _Robert Price_, Sep 07 2017