This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A128509 #7 Oct 19 2017 03:15:06
%S A128509 11,13,13,367,4987,9697,78007,13356127,13356127,6753069187,
%T A128509 218617084627,35679817649197,92975416840027
%N A128509 Initial prime, greater than 7, of a prime chain of length n under the iteration x -> 2x-7.
%C A128509 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 A128509 a(2) = 13 because 13, 13*2-7=19 and 19*2-7=31 are primes.
%t A128509 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 A128509 Cf. A057330, A084954.
%K A128509 nonn,more
%O A128509 1,1
%A A128509 _Zak Seidov_, May 07 2007
%E A128509 Edited by _Stefan Steinerberger_, May 12 2007
%E A128509 Edited by _Don Reble_, Nov 07 2007