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 A139052 #7 Mar 27 2021 14:06:55
%S A139052 2,3,11,13,101,103,1009,1013,10007,10009,100003,100019,1000003,
%T A139052 1000033,10000019,10000079,100000007,100000037,1000000007,1000000009,
%U A139052 10000000019,10000000033,100000000003,100000000019,1000000000039,1000000000061
%N A139052 Array read by rows: row n lists the first two primes with n digits.
%t A139052 ftp[d_]:=Module[{np1=NextPrime[10^(d-1)]},{np1,NextPrime[np1]}]; Array[ ftp,15]//Flatten (* _Harvey P. Dale_, Mar 27 2021 *)
%Y A139052 Cf. A000040, A003617, A073914, A139053, A139054.
%K A139052 base,nonn,tabf
%O A139052 1,1
%A A139052 _Omar E. Pol_, Apr 08 2008
%E A139052 More terms from _Sean A. Irvine_, Jun 02 2011