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 A046275 #14 Oct 10 2019 00:34:15
%S A046275 0,0,0,29,61,9049,53,7829,3046721,89,84401,1381,2429536481,8329,
%T A046275 876792454961,113209,853020188851,77181699666569,15009463529,
%U A046275 35085171767,2157665459056928801,1094189891315123,984770902183
%N A046275 Largest prime substring in 9^n (0 if none).
%H A046275 Harvey P. Dale, <a href="/A046275/b046275.txt">Table of n, a(n) for n = 0..100</a>
%t A046275 lps[n_]:=Module[{c=9^n},Max[Select[FromDigits/@Flatten[Table[ Partition[ IntegerDigits[c],i,1],{i,IntegerLength[c]-1,1,-1}],1],PrimeQ]]]; Join[ {0,0,0},Array[lps,20,3]] (* _Harvey P. Dale_, May 07 2015 *)
%Y A046275 Cf. A046267.
%K A046275 nonn
%O A046275 0,4
%A A046275 _Patrick De Geest_, Jun 15 1998