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 A303448 #14 Apr 24 2018 21:32:21 %S A303448 19781763,46912496118443,192153584101141163 %N A303448 Numbers m such that both m and (m-1)/2 are Fermat pseudoprimes base 2 (A001567). %C A303448 No other terms below 2^65. %C A303448 Terms a(2) and a(3) are of the form (2^(2k+1)+1)/3 = A007583(k). %C A303448 Terms A007583(k) belong to this sequence for k in A303009. Correspondingly, a(4) <= A007583(A303009(3)) = (2^83+1)/3 = 3223802185639011132549803. %C A303448 If a(n) is not divisible by 3, then it also belongs to A175625. %F A303448 a(n) = 2*A303447(n) + 1. %Y A303448 Numbers (a(n)-1)/2 are listed in A303447. %Y A303448 Subsequence of A006970 and A300193. %Y A303448 Cf. A175625, A175942, A298758. %K A303448 bref,hard,more,nonn %O A303448 1,1 %A A303448 _Max Alekseyev_, Apr 24 2018 %E A303448 a(1) from _Amiram Eldar_, Jan 26 2018