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 A099630 #5 Jun 04 2018 20:23:09
%S A099630 11,11,101,997,1009,9973,10007,99991,100003,999983,1000003,9999991,
%T A099630 10000019,99999989,100000007,999999937,1000000007,9999999967,
%U A099630 10000000019,99999999977,100000000003,999999999989,1000000000039,9999999999971,10000000000037,99999999999973
%N A099630 Smallest and largest primes pairwise displayed with k digits from k=2,3,... with repeated decimal digits.
%C A099630 Contrary to A099629, this sequence is evidently infinite. Essentially [for more than 2 digits] consists of pairs of {nextprime[10^j],prevprime[10^(j+1)]}.
%t A099630 Join[{11,11},Flatten[Table[{NextPrime[10^n],NextPrime[10^(n+1),-1]}, {n,2,20}]]] (* _Harvey P. Dale_, Jun 04 2018 *)
%Y A099630 Cf. A098224-A098227.
%K A099630 base,nonn
%O A099630 1,1
%A A099630 _Labos Elemer_, Oct 26 2004
%E A099630 Corrected and extended by _Harvey P. Dale_, Jun 04 2018