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 A004249 (2^2^...^2) (with n 2's) + 1. 7
 2, 3, 5, 17, 65537 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 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. REFERENCES P. Ribenboim, The Book of Prime Number Records. Springer-Verlag, NY, 2nd ed., 1989, p. 73. LINKS Y. Bugeaud and M. Queffélec, On Rational Approximation of the Binary Thue-Morse-Mahler Number, Journal of Integer Sequences, 16 (2013), #13.2.3. Wilfrid Keller, Prime factors k.2^n + 1 of Fermat numbers F_m FORMULA a(0) = 1, a(n+1) = 2^(a(n)) for n >= 0. a(n) = A014221(n+1)+1. - Leroy Quet, Jun 10 2009 CROSSREFS Cf. Fermat numbers 2^2^n + 1 = A000215. A007516 is another version. Sequence in context: A127063 A127837 A253646 * A268210 A121510 A132346 Adjacent sequences:  A004246 A004247 A004248 * A004250 A004251 A004252 KEYWORD nonn AUTHOR STATUS approved

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Last modified March 20 17:13 EDT 2019. Contains 321345 sequences. (Running on oeis4.)