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 A124493 #8 Mar 27 2020 09:02:40
%S A124493 3,6,21,45,90,180,255,360,510,516,615,705,726,741,756,906,945,951,966,
%T A124493 1230,1350,1410,1725,1746,1770,1911,1956,2541,2700,2721,2925,3051,
%U A124493 3066,3225,3540,3576,3675,3951,4485,4611,5295,5346,5355,5586,5736,5775,5901
%N A124493 Numbers k for which 2*k-1, 4*k-1 and 8*k-1 are primes.
%H A124493 Amiram Eldar, <a href="/A124493/b124493.txt">Table of n, a(n) for n = 1..10000</a>
%t A124493 Select[3*Range[2000], And @@ PrimeQ /@ ({2, 4, 8}*# - 1) &] (* _Ray Chandler_, Nov 22 2006 *)
%Y A124493 Cf. A006254, A124485, A124494, A124017, A125113, A124514, A124515, A124516.
%K A124493 nonn
%O A124493 1,1
%A A124493 _Artur Jasinski_, Nov 04 2006