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 A139536 #9 Aug 07 2021 13:24:23
%S A139536 101,1009,10007,100003,1000003,100000037,100000007,1000000007,
%T A139536 100000000019,100000000003,10000000000037,100000000000031,
%U A139536 1000000000000037,10000000000000061,100000000000000013
%N A139536 Smallest prime starting with 1 and followed by a string of n 0's.
%C A139536 Not the same as A139535 though most entries match. (First dissimilarity occurs for n=19: A139535(19)=1000000000000000000409; A139536(19)=10000000000000000000139.)
%H A139536 Harvey P. Dale, <a href="/A139536/b139536.txt">Table of n, a(n) for n = 1..997</a>
%t A139536 Table[Module[{k=1},While[CompositeQ[10^IntegerLength[k] FromDigits[ PadRight[ {1},n,0]]+k],k+=2];10^IntegerLength[k] FromDigits[ PadRight[ {1},n,0]]+k],{n,2,20}] (* _Harvey P. Dale_, Aug 07 2021 *)
%K A139536 nonn,base
%O A139536 1,1
%A A139536 _Lekraj Beedassy_, Apr 25 2008