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 A291998 #9 Nov 11 2019 13:48:32
%S A291998 521,31,601,19531,12207031,390001,305175781,234750601,
%T A291998 60081451169922001,152587500001,10910444855403996246103496881,
%U A291998 59509429687890001,11293772630057337854244300009061892827351888021,9080418348371887359375390001,5465713352000770660547109750601
%N A291998 Primes of the form Phi(k, -5), where Phi is the cyclotomic polynomial.
%H A291998 Robert Price, <a href="/A291998/b291998.txt">Table of n, a(n) for n = 1..31</a>
%H A291998 Yves Gallot, <a href="http://yves.gallot.pagesperso-orange.fr/papers/cyclotomic.html">Cyclotomic polynomials and prime numbers</a>
%H A291998 <a href="/index/Cy#CyclotomicPolynomialsValuesAtX">Index entries for cyclotomic polynomials,values at X</a>
%t A291998 Select[Table[Cyclotomic[k,-5], {k, 0, 100}], PrimeQ[#] &]
%Y A291998 Cf. A138925.
%K A291998 nonn
%O A291998 1,1
%A A291998 _Robert Price_, Sep 07 2017