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.

127, 607, 4423, 216091, 1398269, 3021377

Offset

1,1

Links

Table of n, a(n) for n=1..6.

Formula

{A000043(i): A134458(i) >= A000043(i)}. - R. J. Mathar, Dec 20 2008

Example

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.)

Mathematica

s={}; Do[If[MersennePrimeExponent[k+1] > 2 * MersennePrimeExponent[k], AppendTo[s, MersennePrimeExponent[k]]], {k, 1, 44}]; s (* Amiram Eldar, Feb 03 2019 *)

Crossrefs

Cf. A000043, A134458.

Sequence in context: A096523 A299132 A142736 * A299890 A200813 A332574

Adjacent sequences: A152780 A152781 A152782 * A152784 A152785 A152786

Keyword

nonn,more

Author

J. Lowell, Dec 12 2008

Extensions

Edited by R. J. Mathar, Dec 20 2008

a(5) inserted by Amiram Eldar, Feb 03 2019

Status

approved