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A019434 List of Fermat primes: primes of form 2^(2^k) + 1, for some k >= 0. +0
92
3, 5, 17, 257, 65537 (list; graph; listen)
OFFSET

1,1

REFERENCES

G. Everest, A. van der Poorten, I. Shparlinski and T. Ward, Recurrence Sequences, Amer. Math. Soc., 2003; see esp. p. 255.

R. K. Guy, Unsolved Problems in Number Theory, A3.

LINKS

C. Banderier, Pepin's Criterion For Fermat Numbers

C. K. Caldwell, The Prime Glossary, Fermat prime

Wilfrid Keller, Prime factors k.2^n + 1 of Fermat numbers F_m

Eric Weisstein's World of Mathematics, Link to a section of The World f Mathematics

Eric Weisstein's World of Mathematics, Fermat Number

Eric Weisstein's World of Mathematics, Fermat Prime

Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics

Wikipedia, Fermat prime

MATHEMATICA

Table[2^(2^n)+1, {n, 0, 4}] (from Vladimir Orlovsky (4vladimir(AT) gmail.com), Apr 29 2008)

PROGRAM

(PARI) for(i=0, 99, isprime(2^2^i+1) & print1(2^2^i+1, ", ")) \\ - M. F. Hasler, Nov 21 2009

CROSSREFS

Cf. A000215, A159611.

Sequence in context: A023394 A056130 A078726 this_sequence A164307 A125045 A093179

Adjacent sequences: A019431 A019432 A019433 this_sequence A019435 A019436 A019437

KEYWORD

nonn,nice,new

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com), David W. Wilson (davidwwilson(AT)comcast.net)

EXTENSIONS

It is conjectured that there are only 5 terms. Currently it has been shown that 2^(2^k) + 1 is composite for 5<=k<=32 (see Eric Weisstein's Fermat Primes link. - Dmitry Kamenetsky (dkamen(AT)rsise.anu.edu.au), Sep 28 2008

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Last modified December 11 12:57 EST 2009. Contains 170656 sequences.


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