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 A104088 #10 Jun 20 2021 16:30:07
%S A104088 3,7,23,79,241,727,2179,6553,19681,59029,177131,531383,1594301,
%T A104088 4782961,14348891,43046623,129140153,387420479,1162261453,3486784393,
%U A104088 10460353199,31381059607,94143178807,282429536453,847288609423
%N A104088 Largest prime <= 3^n.
%t A104088 PrimePrev[n_]:=Module[{k=n},While[ !PrimeQ[k],k-- ];k];f[n_]:=3^n;lst={};Do[AppendTo[lst,PrimePrev[f[n]]],{n,5!}];lst (* _Vladimir Joseph Stephan Orlovsky_, Feb 26 2010 *)
%t A104088 Join[{3},NextPrime[3^Range[2,50],-1]] (* _Harvey P. Dale_, Jun 20 2021 *)
%o A104088 (PARI) g(n,b) = for(x=0,n,print1(precprime(b^x)","))
%K A104088 easy,nonn
%O A104088 1,1
%A A104088 _Cino Hilliard_, Mar 03 2005