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A004249
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(2^2^...^2) (with n 2's) + 1.
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5
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OFFSET
| 0,1
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COMMENTS
| a(0) could equally well be taken to be 1 rather than 2, which gives A007516. - N. J. A. Sloane, Sep 14 2009
A subsequence of the Fermat numbers 2^2^n + 1 = A000215.
a(0) through a(4) are primes; a(5) = 2^65536 + 1 is divisible by 825753601.
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REFERENCES
| P. Ribenboim, The Book of Prime Number Records. Springer-Verlag, NY, 2nd ed., 1989, p. 73.
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LINKS
| Wilfrid Keller, Prime factors k.2^n + 1 of Fermat numbers F_m
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FORMULA
| a[0] := 1, a[n+1] := 2^(a[n]) for n >= 0.
a(n) = A014221(n+1)+1. - Leroy Quet, Jun 10 2009
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CROSSREFS
| Cf. Fermat numbers 2^2^n + 1 = A000215. A007516 is another version.
Sequence in context: A092506 A127063 A127837 * A121510 A132346 A041293
Adjacent sequences: A004246 A004247 A004248 * A004250 A004251 A004252
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com), David W. Wilson (davidwwilson(AT)comcast.net)
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