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Initial prime, greater than 7, of a prime chain of length n under the iteration x -> 2x-7.
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%I #7 Oct 19 2017 03:15:06

%S 11,13,13,367,4987,9697,78007,13356127,13356127,6753069187,

%T 218617084627,35679817649197,92975416840027

%N Initial prime, greater than 7, of a prime chain of length n under the iteration x -> 2x-7.

%C From the definition we see that the sequence is monotonic (but not strictly) increasing. The sequence is a generalized Cunningham chain. - _Stefan Steinerberger_, May 12 2007

%e a(2) = 13 because 13, 13*2-7=19 and 19*2-7=31 are primes.

%t k = 5; For[n = 2, n <= 10, n++, While[Union[PrimeQ[NestList[2# - 7 &, Prime[k], n]], PrimeQ[NestList[2# - 7 &, Prime[k], n]]] != {True}, k++ ]; Print[Prime[k]]] (* _Stefan Steinerberger_, May 12 2007 *)

%Y Cf. A057330, A084954.

%K nonn,more

%O 1,1

%A _Zak Seidov_, May 07 2007

%E Edited by _Stefan Steinerberger_, May 12 2007

%E Edited by _Don Reble_, Nov 07 2007