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A049883 Primes in the Jacobsthal sequence (A001045). 7
3, 5, 11, 43, 683, 2731, 43691, 174763, 2796203, 715827883, 2932031007403, 768614336404564651, 201487636602438195784363, 845100400152152934331135470251, 56713727820156410577229101238628035243 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

All a(n), except a(2) = 5, are of the form (2^p + 1)/3 - the Wagstaff primes A000979[n] = {3,11,43,683,2731,43691,174763,...}.

Indices of prime Jacobsthal numbers are listed in A107036[n] = {3,4,5,7,11,13,17,19,23,31,43,61,...}.

For n>1 A107036[n] = A000978[n] Numbers n such that (2^n + 1)/3 is prime. - Alexander Adamchuk, Oct 10 2006

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..23

MATHEMATICA

Select[Table[(2^n + (-1)^(n - 1))/3, {n, 200}], PrimeQ] (* Vladimir Joseph Stephan Orlovsky, Mar 29 2011*)

CROSSREFS

Cf. A001045, A107036, A000978, A000979.

Sequence in context: A236457 A105236 A144467 * A059242 A175173 A004203

Adjacent sequences:  A049880 A049881 A049882 * A049884 A049885 A049886

KEYWORD

nonn

AUTHOR

Judson D. Neer (judson(AT)poboxes.com)

STATUS

approved

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Last modified December 20 19:29 EST 2014. Contains 252289 sequences.