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 A066622 #9 Oct 02 2022 18:12:45
%S A066622 2,232,23532,2357532,2357117532,23571113117532,235711131713117532,
%T A066622 2357111317191713117532,23571113171923191713117532,
%U A066622 235711131719232923191713117532,2357111317192329312923191713117532
%N A066622 Concatenation of prime numbers in increasing order up to the n-th and then in decreasing order.
%H A066622 Harvey P. Dale, <a href="/A066622/b066622.txt">Table of n, a(n) for n = 1..174</a>
%t A066622 Table[FromDigits[Flatten[IntegerDigits/@Join[Prime[Range[n]],Reverse[Most[Prime[Range[n]]]]]]],{n,12}] (* _Harvey P. Dale_, Oct 02 2022 *)
%K A066622 easy,nonn,base
%O A066622 1,1
%A A066622 _Amarnath Murthy_, Dec 25 2001
%E A066622 More terms from _Sascha Kurz_, Mar 23 2002