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 A231235 #20 Jun 06 2021 15:22:24 %S A231235 93738231893,2365771484804813,4185535280578373,4658429282719973, %T A231235 7706774555568173,7711174427503853,25756066576859093, %U A231235 65522912397466973,80107252841869013,105371595617867573,130831138562692133,174460360753737533,201928181545454813,204300010667474573 %N A231235 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 A231235 The next iteration is impossible: t^2 + 4 is divisible by 13. %H A231235 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 A231235 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 A231235 Subsequence of A231120 and A165218. %Y A231235 Cf. A116889. %K A231235 nonn %O A231235 1,1 %A A231235 _Zak Seidov_, Nov 06 2013 %E A231235 Definition corrected by _Harvey P. Dale_, Jun 06 2021