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 A211876 #24 Aug 22 2019 12:03:24
%S A211876 3,5,11,13,17,241,257,331,683,5419,61681,65537,2796203,15790321,
%T A211876 22366891,4278255361,4562284561,77158673929,1133836730401,
%U A211876 18446744069414584321,291280009243618888211558641,78919881726271091143763623681,84159375948762099254554456081,84179842077657862011867889681
%N A211876 Primes of the form Phi(phi(k),2), the phi(k)-th cyclotomic polynomial evaluated at 2, where phi is the Euler totient function.
%t A211876 s = Union[Table[EulerPhi[n], {n, 2000}]]; t = Union[Select[Table[ Cyclotomic[ n, 2], {n, s}], PrimeQ]]; Select[t, # < 10^30 &]
%o A211876 (PARI)
%o A211876 s=Set([]);
%o A211876 for (n=1,10^3, my(a=polcyclo(eulerphi(n),2)); if(ispseudoprime(a), s=setunion(s,[a])));
%o A211876 v211876=s /* _Joerg Arndt_, Apr 13 2013 */
%Y A211876 Cf. A000010, A211875, A211874.
%K A211876 nonn
%O A211876 1,1
%A A211876 _Alexander Gruber_, Feb 12 2013