%I A057331
%S A057331 2,2,2,2,2,89,1122659,19099919,85864769,26089808579,554688278429,4090932431513069
%N A057331 a(n) = smallest prime p such that the first n iterates of p under x->
               2x+1 are all primes.
%C A057331 Initial terms of A000040, A005384, A007700, A023272, A023302, A023330.
%C A057331 For n>10 a(n) == -1 (mod 2*3*5*11*13). - Farideh Firoozbakht (mymontain(AT)yahoo.com), 
               Apr 24 2004
%H A057331 C. K. Caldwell, <a href="http://primes.utm.edu/glossary/page.php?sort=CunninghamChain">
               Latest results about Cunningham Chains</a>
%H A057331 <a href="Sindx_Pri.html#primes_AP">Index entries for sequences related 
               to primes in arithmetic progressions</a>
%e A057331 a(5) = 89 because the numbers 89, 179, 359, 719, 1439, 2879 are all primes 
               and 89 is the first number to have this property.
%t A057331 f[n_] := 2n + 1; k = 1; Do[ While[ Union[ PrimeQ[ NestList[ f, Prime[k], 
               n]]] != {True}, k++ ]; Print[ Prime[k]], {n, 1, 9} ]
%Y A057331 See also A005602.
%Y A057331 Sequence in context: A060359 A029665 A056993 this_sequence A067089 A090872 
               A063473
%Y A057331 Adjacent sequences: A057328 A057329 A057330 this_sequence A057332 A057333 
               A057334
%K A057331 nonn,nice
%O A057331 0,1
%A A057331 Patrick De Geest (pdg(AT)worldofnumbers.com), Aug 15 2000.
%E A057331 More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Apr 24 
               2004
%E A057331 a(13) (from the Caldwell link) sent by Peter Deleu, Hulste, Belgium, 
               Nov 22, 2004