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 A173831 #6 Dec 08 2018 17:19:33
%S A173831 13,79,251,619,1291,2399,4093,6553,9973,14639,20731,28559,38393,50599,
%T A173831 65521,83497,104971,130307,159979,194479,234239,279823,331769,390581,
%U A173831 456959,531383,614639,707279,809993,923513,1048573,1185907,1336333
%N A173831 Largest prime < n^4.
%t A173831 PrimePrev[n_]:=Module[{k},k=n-1;While[ !PrimeQ[k],k-- ];k];f[n_]:=n^4;lst={};Do[AppendTo[lst,PrimePrev[f[n]]],{n,5!}];lst
%t A173831 NextPrime[Range[2,40]^4,-1] (* _Harvey P. Dale_, May 05 2018 *)
%Y A173831 Cf. A014220, A053001, A077037
%K A173831 nonn
%O A173831 2,1
%A A173831 _Vladimir Joseph Stephan Orlovsky_, Feb 25 2010