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 A339818 #12 Dec 26 2020 16:06:22
%S A339818 1729,15841,3057601,3828001,5310721,8355841,8830801,9439201,14676481,
%T A339818 15829633,17236801,40280065,78091201,83099521,84350561,92625121,
%U A339818 94536001,104852881,118901521,129762001,157731841,163954561,180115489,193708801,214852609,221884001,279377281,382304161,382536001,438359041,481239361,511338241
%N A339818 Carmichael numbers k for which the 2-adic valuation of phi(k) does not exceed the 2-adic valuation of k-1.
%H A339818 Amiram Eldar, <a href="/A339818/b339818.txt">Table of n, a(n) for n = 1..22784</a> (terms below 2^64)
%t A339818 carmichaels = Cases[Import["https://oeis.org/A002997/b002997.txt", "Table"], {_, _}][[;; , 2]]; q[n_] := IntegerExponent[EulerPhi[n], 2] <= IntegerExponent[n - 1, 2]; Select[carmichaels, q] (* _Amiram Eldar_, Dec 26 2020 *)
%o A339818 (PARI)
%o A339818 A002322(n) = lcm(znstar(n)[2]); \\ From A002322
%o A339818 isA339818(n) = ((n>1)&&issquarefree(n)&&!isprime(n)&&(valuation(eulerphi(n),2)<=valuation(n-1,2))&&(0==((n-1)%A002322(n))));
%Y A339818 Intersection of A002997 and A339817 (see comments in latter).
%Y A339818 Cf. also A339869, A339878, A339909.
%K A339818 nonn
%O A339818 1,1
%A A339818 _Antti Karttunen_, Dec 20 2020