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 A277720 #28 Apr 21 2024 09:59:48 %S A277720 2320690177,17069520863233,42182344790209,65465530560001, %T A277720 3432376805760001,13322002122777601,20388795375960001, %U A277720 129009714848870401,580007888606160001,1096591987029196801,3029756968906340401,5806765663003468801,6213994663149504001,6367205158826803201,7802569551798000001,10319507991273499201 %N A277720 Numbers k > 2 such that lambda(k)^2 divides k-1, where lambda(k) = A002322(k). %C A277720 Squarefree numbers k > 2 such that (p-1)^2 | k-1 for every prime p|k. %C A277720 For the first five terms, lambda(k)^2 | phi(k). - _Thomas Ordowski_, Apr 11 2017 %H A277720 Amiram Eldar, <a href="/A277720/b277720.txt">Table of n, a(n) for n = 1..47</a> (terms below 10^22, calculated using data from Claude Goutier) %H A277720 Claude Goutier, <a href="http://www-labs.iro.umontreal.ca/~goutier/OEIS/A055553/">Compressed text file carm10e22.gz containing all the Carmichael numbers up to 10^22</a>. %o A277720 (PARI) isok(n) = (n % lcm(znstar(n)[2])^2) == 1; \\ _Michel Marcus_, Apr 22 2017 %Y A277720 Subsequence of A002997 and of A277389. %Y A277720 Cf. A002322. %K A277720 nonn %O A277720 1,1 %A A277720 _Thomas Ordowski_ and _Charles R Greathouse IV_, Oct 28 2016 %E A277720 a(7)-a(16) from _Max Alekseyev_, Apr 23 2017