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 A128458 #19 Jun 11 2021 08:45:19
%S A128458 1,2,3,7,12,17,19,51,65,550,1460,1641,7035,18002,20963,21163,42563,
%T A128458 94906,148048
%N A128458 Numbers k such that 15^k - 2 is a prime.
%C A128458 a(20) > 2*10^5. - _Robert Price_, Jun 23 2015
%t A128458 Do[ f = 15^n - 2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n,1,1000} ]
%t A128458 Do[If[PrimeQ[15^n - 2], Print[n]], {n, 10^4}] (* _Ryan Propper_, Jun 06 2007 *)
%Y A128458 Cf. A084714 (smallest prime of the form (2n-1)^k - 2).
%Y A128458 Cf. A128472 (smallest prime of the form (2n-1)^k - 2 for k > (2n-1)).
%Y A128458 Cf. A014224, A109080, A090669, A128455, A128457, A128459, A128460, A128461.
%K A128458 nonn,hard,more
%O A128458 1,2
%A A128458 _Alexander Adamchuk_, Mar 14 2007
%E A128458 550 from _Stefan Steinerberger_, May 05 2007
%E A128458 3 more terms from _Ryan Propper_, Jun 06 2007
%E A128458 a(14)-a(19) from _Robert Price_, Jun 23 2015