A156893 Primes of the form 1 + 2 * Product_{i=1..k} (2^i-1).

3, 7, 43, 631, 19531, 1230391, 39846180151, 42638416803867688651, 1430183959005766573513154251

Offset

1,1

Comments

Primes of the form 2*A005329(k)+1.

Links

Robert Israel, Table of n, a(n) for n = 1..12

Example

For n=4, 2*(2^1 - 1)*(2^2 - 1)*(2^3 -1)*(2^4 - 1) + 1 = 2*1*3*7*15 + 1 = 631

Maple

R:= NULL: count:= 0: v:= 1:
for k from 1 while count < 10 do
  v:= v*(2^k-1);
  p:= 1+2*v;
  if isprime(p) then R:= R, p; count:= count+1 fi
od:
R; # Robert Israel, May 04 2023

Crossrefs

Sequence in context: A181729 A162455 A143684 * A050639 A280717 A100837

Adjacent sequences: A156890 A156891 A156892 * A156894 A156895 A156896

Keyword

nonn

Author

J. M. Bergot, Feb 17 2009

Extensions

Definition and terms corrected by R. J. Mathar, Jul 10 2011

Status

approved