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 A152783 #13 Jun 19 2021 04:50:50
%S A152783 127,607,4423,216091,1398269,3021377
%N A152783 Values of p for which 2^p - 1 is prime and which are followed by a gap such that no 2^q - 1 is prime for p < q < 2*p.
%F A152783 {A000043(i): A134458(i) >= A000043(i)}. - _R. J. Mathar_, Dec 20 2008
%e A152783 127 is in this sequence because 2^127-1 is prime, but no value of 2^q-1 is prime for q > 127 and q <= 254. (The next value of q to yield a prime is 521 and is outside the (127,254] interval.)
%t A152783 s={}; Do[If[MersennePrimeExponent[k+1] > 2 * MersennePrimeExponent[k], AppendTo[s, MersennePrimeExponent[k]]], {k, 1, 44}]; s (* _Amiram Eldar_, Feb 03 2019 *)
%Y A152783 Cf. A000043, A134458.
%K A152783 nonn,more
%O A152783 1,1
%A A152783 _J. Lowell_, Dec 12 2008
%E A152783 Edited by _R. J. Mathar_, Dec 20 2008
%E A152783 a(5) inserted by _Amiram Eldar_, Feb 03 2019