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 A187730 #26 Oct 11 2019 16:53:20
%S A187730 1,1,2,1,4,1,6,1,2,1,10,1,12,1,2,1,16,1,18,1,2,1,22,1,4,1,2,3,28,1,30,
%T A187730 1,2,1,2,1,36,1,2,1,40,1,42,1,4,1,46,1,6,1,2,3,52,1,2,1,2,1,58,1,60,1,
%U A187730 2,1,4,5,66,1,2,3,70,1,72,1,2,3,2,1,78,1
%N A187730 Greatest common divisor of Carmichael lambda(n) and n - 1.
%C A187730 n is a Giuga number and A002322(n)/a(n) divides k if and only if 1^(k*(n-1)) + 2^(k*(n-1)) +...+ (n-1)^(k*(n-1)) = -1 (mod n).
%H A187730 Amiram Eldar, <a href="/A187730/b187730.txt">Table of n, a(n) for n = 1..10000</a>
%H A187730 J. M. Grau and Antonio Oller-Marcén, <a href="http://arxiv.org/abs/1103.3483">Generalizing Giuga's conjecture</a>, arXiv:1103.3483 [math.NT], 2011.
%t A187730 Table[GCD[CarmichaelLambda[n],n-1],{n,100}]
%o A187730 (PARI) a(n) = gcd(lcm(znstar(n)[2]), n-1); \\ _Michel Marcus_, Mar 18 2016
%Y A187730 Cf. A002322 (Carmichael lambda function).
%K A187730 nonn
%O A187730 1,3
%A A187730 _José María Grau Ribas_, Mar 13 2011