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%I #20 Jun 06 2021 15:22:24
%S 93738231893,2365771484804813,4185535280578373,4658429282719973,
%T 7706774555568173,7711174427503853,25756066576859093,
%U 65522912397466973,80107252841869013,105371595617867573,130831138562692133,174460360753737533,201928181545454813,204300010667474573
%N Primes q of the form p^2 + 4 (p prime) such that r = q^2 + 4, s = r^2 + 4 and t = s^2 + 4 are all prime.
%C The next iteration is impossible: t^2 + 4 is divisible by 13.
%H Zak Seidov and Charles R Greathouse IV, <a href="/A231235/b231235.txt">Table of n, a(n) for n = 1..250</a> (first 100 terms from Zak Seidov)
%t extnd[p_]:=NestList[#^2+4&,p,4]; #^2+4&/@Select[Prime[ Range[ 452*10^6]],AllTrue[Rest[extnd[#]],PrimeQ]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 06 2021 *)
%Y Subsequence of A231120 and A165218.
%Y Cf. A116889.
%K nonn
%O 1,1
%A _Zak Seidov_, Nov 06 2013
%E Definition corrected by _Harvey P. Dale_, Jun 06 2021