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 A366822 #11 Feb 16 2025 08:34:06
%S A366822 1,1,4,12,256,1040,41472,407680,16515072,152845056,9897840000,
%T A366822 89493288192,8732596764672,129785922489600,10576701872701440,
%U A366822 210729768933600000,18446676793287966720,275746753962112254720,28084363369373740400640,791359800910482004224000
%N A366822 a(n) is phi(n^n + 1) where phi is the Euler totient function.
%H A366822 Robert G. Wilson v, <a href="/A366822/b366822.txt">Table of n, a(n) for n = 0..72</a>
%H A366822 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SierpinskiNumberoftheFirstKind.html">Sierpinski Number of the First Kind</a>
%F A366822 a(n) = A000010(A014566(n)).
%t A366822 {1}~Join~Array[EulerPhi[#^# + 1] &, 19] (* _Michael De Vlieger_, Oct 24 2023 *)
%o A366822 (PARI) a(n) = eulerphi(n^n+1);
%Y A366822 Cf. A000010, A014566, A064447, A366821.
%K A366822 nonn
%O A366822 0,3
%A A366822 _Sean A. Irvine_, Oct 24 2023