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 A105428 #15 Jan 17 2019 13:44:08
%S A105428 7,31,67,151,23,13,7,157,163,107,17,13,7,89,170809,31,13,7,4363363,
%T A105428 251,42169,43,13,7,641,17,6791,109,13,7,31,29,373,261382937,13,7,
%U A105428 101921,82647847,443,13,7,43,1042402171,71,31,13,7,1601,425519761
%N A105428 Smallest prime dividing the composite near-repdigit number 133...33 consisting of a 1 followed by n 3's, where n=A105427.
%H A105428 FactorDB, <a href="http://factordb.com/index.php?query=(10%5En-1)%2F3%2B10%5En">Factorizations of (10^n-1)/3+10^n</a>
%H A105428 Makoto Kamada, <a href="https://stdkmd.net/nrr/1/13333.htm">Factorizations of 133...33</a>.
%t A105428 Transpose[FactorInteger[#]][[1,1]]&/@DeleteCases[Table[ FromDigits[ PadRight[{1},n,3]],{n,2,60}],_?PrimeQ] (* _Harvey P. Dale_, Dec 10 2011 *)
%o A105428 (PARI) for(n=1,100,m=10^n+(10^n-1)/3;if(!isprime(m),print1(factorint(m)[1,1]," "))) (Alekseyev)
%Y A105428 Cf. A089018.
%K A105428 nonn
%O A105428 1,1
%A A105428 _Lekraj Beedassy_, Apr 08 2005
%E A105428 More terms from _Max Alekseyev_, Apr 11 2005