

A058220


Ultrauseful primes: smallest k such that 2^(2^n)  k is prime.


3



1, 3, 5, 15, 5, 59, 159, 189, 569, 105, 1557, 2549, 2439, 13797, 25353, 5627, 24317
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OFFSET

1,2


COMMENTS

2^(2^16)5627 was found by Joel Levy in Feb 2004.  Donovan Johnson, Sep 13 2008


LINKS

Table of n, a(n) for n=1..17.


MATHEMATICA

np[n_]:=Module[{x=2^(2^n)}, xNextPrime[x, 1]]; Array[np, 17] (* Harvey P. Dale, Jun 04 2011 *)


CROSSREFS

Cf. A058221.
Sequence in context: A270688 A270453 A270464 * A100181 A180620 A277323
Adjacent sequences: A058217 A058218 A058219 * A058221 A058222 A058223


KEYWORD

nonn,hard,nice


AUTHOR

Warren D. Smith, Nov 30 2000


EXTENSIONS

a(16)a(17) from Donovan Johnson, Sep 13 2008


STATUS

approved



