OFFSET
1,1
COMMENTS
The corresponding indices k are 2, 4, 5, 8, 77, 377, 4547, ... (see A200818).
The generalization of this sequence is possible with the primes of the form (b^n +- k)*b^n +- 1.
For k = 377, a(6) contains 227 digits;
For k = 4547, a(7) contains 2738 digits;
For k = 8248, a(8) contains 4966 digits.
LINKS
Henri Lifchitz, New forms of primes
EXAMPLE
191 is in the sequence because, for k=4, (2^4 - 4)*2^4 - 1 = 191 is prime.
MATHEMATICA
a={}; Do[p=(2^n-n)*2^n-1; If[PrimeQ[p], AppendTo[a, p]], {n, 10^3}]; Print[a]
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Michel Lagneau, Nov 23 2011
EXTENSIONS
a(8) from L. Joris Perrenet, Mar 17 2020
STATUS
approved