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 A131306 #10 Aug 28 2016 19:03:17
%S A131306 2,11,1777,23333,199999,2999999,19999999,577777777,1777777777,
%T A131306 23333333333,311111111111,2111111111111,17777777777777,
%U A131306 499999999999999,1333333333333333,23333333333333333
%N A131306 Smallest prime ending with exactly n identical digits.
%C A131306 By Dirichlet's theorem, there is a prime for each n. For the n in A004023, the smallest prime consists of all ones. - T. D. Noe, Oct 01 2007
%H A131306 T. D. Noe, <a href="/A131306/b131306.txt">Table of n, a(n) for n=1..200</a>
%e A131306 a(4)=23333 because 23333 is the smallest prime ending with exactly 4 identical digits.
%t A131306 sp[n_]:=Module[{k=1},While[!PrimeQ[k*10^IntegerLength[n]+n],k++];k*10^IntegerLength[n]+n]; Join[{2,11},Table[Min[sp/@FromDigits/@ Table[PadRight[{},i,n],{n,{1,3,7,9}}]],{i,3,20}]] (* _Harvey P. Dale_, Aug 28 2016 *)
%K A131306 base,nonn
%O A131306 1,1
%A A131306 _Shyam Sunder Gupta_, Sep 29 2007