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 A122528 Minimal number k such that (2k)^(2^n) + 1 is prime, but (2k)^(2^m) + 1 is composite for m < n. 1
 1, 7, 17, 76, 22, 57, 137, 117, 307, 671, 412, 1279, 767, 35926, 50915, 35453, 24297, 114094, 12259, 37949, 459722 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS A079706(a(n)) = 2^n which is the first occurrence of 2^n in A079706. Corresponding primes A084712(a(n)) are {3, 197, 1336337, 284936905588473857, 197352587024076973231046657, ...}. LINKS Yves Gallot et al., Generalized Fermat Prime Search PrimeGrid, GFN Prime Search Status and History. EXAMPLE a(0) = 1 because (2*1)^(2^0) + 1 = 2 + 1 = 3 is prime. a(1) = 7 because (2*7)^(2^1) + 1 = 14^2 + 1 = 197 is prime but 14 + 1 = 15 is composite. PROG (PARI) a(n)=for(k=1, +oo, if(ispseudoprime((2*k)^(2^n)+1), for(m=0, n-1, ispseudoprime((2*k)^(2^m)+1)&&next(2)); return(k))) \\ Jeppe Stig Nielsen, Mar 10 2018 CROSSREFS Cf. A079706, A084712. Cf. A056993. Sequence in context: A086870 A107693 A217717 * A123206 A035078 A177123 Adjacent sequences:  A122525 A122526 A122527 * A122529 A122530 A122531 KEYWORD hard,more,nonn AUTHOR Alexander Adamchuk, Sep 17 2006 EXTENSIONS Definition corrected by T. D. Noe, May 14 2008 a(9) through a(16) from the extensive tables of generalized Fermat primes compiled by Yves Gallot and others. - T. D. Noe, May 14 2008 a(17)-a(20) from Jeppe Stig Nielsen, Mar 10 2018 STATUS approved

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Last modified May 12 07:21 EDT 2021. Contains 343821 sequences. (Running on oeis4.)