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 A109799 #23 Mar 31 2024 13:53:52 %S A109799 2,3,5,7,13,17,19,31,61,127 %N A109799 Primes p such that 2^p - 1 is a Chen prime. %C A109799 For p in this sequence, 2^p - 1 is called a Mersenne-Chen prime. %C A109799 Conjecture: 2^127 - 1 is the largest Mersenne-Chen prime. %C A109799 Except for the initial term 2, this sequence is the intersection of A000043 and A000978 given by A107360. - _Max Alekseyev_, Oct 28 2008, Jan 28 2010 %e A109799 a(5)=13 because 2^13 - 1 = 8191 is prime and 2^13 + 1 = 3*2731 is semiprime. %t A109799 Select[Prime[Range[40]],PrimeQ[2^#-1]&&PrimeOmega[2^#+1]<3&] (* _James C. McMahon_, Mar 30 2024 *) %Y A109799 Cf. A000043, A000978, A107360, A109611. %K A109799 hard,more,nonn %O A109799 1,1 %A A109799 _Jason Earls_, Aug 15 2005