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 A030456 #40 Apr 01 2020 21:47:16
%S A030456 2,23,223,1223,12239,122393,1223939,12239393,122393939,1223939399,
%T A030456 12239393993,122393939933,12239393993311,412239393993311,
%U A030456 8412239393993311,78412239393993311,2378412239393993311,23784122393939933111,2623784122393939933111,26237841223939399331111
%N A030456 a(0) = 2; a(n) is smallest prime containing a(n-1) as substring.
%H A030456 Sean A. Irvine, <a href="/A030456/b030456.txt">Table of n, a(n) for n = 0..100</a> (first 17 terms from Zak Seidov)
%H A030456 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a030/A030456.java">Java program</a> (github)
%t A030456 FromDigits /@ Nest[Append[#, Block[{p = NextPrime@ FromDigits@ #[[-1]], d}, While[Length@ SequencePosition[Set[d, IntegerDigits@ p], #[[-1]]] == 0, p = NextPrime@ p]; d]] &, {{2}}, 7] (* _Michael De Vlieger_, Feb 26 2018 *)
%Y A030456 Cf. A068167.
%K A030456 nonn,base
%O A030456 0,1
%A A030456 _Patrick De Geest_
%E A030456 a(17) onward from _Zak Seidov_, Nov 02 2009
%E A030456 a(19) corrected by _Andrew Howroyd_, Feb 26 2018
%E A030456 a(17) onward corrected by _Sean A. Irvine_, Apr 01 2020