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 A104458 #4 Jul 23 2018 12:48:24
%S A104458 2,3,23,323,23323,32323323,2332332323323,323233232332332323323,
%T A104458 2332332323323323233232332332323323,
%U A104458 3232332323323323233232332332323323323233232332332323323,23323323233233232332323323323233233232332323323323233232332332323323323233232332332323323
%N A104458 Define the first two terms to be 2 and 3. All the other terms are obtained by concatenating the two previous terms.
%e A104458 The third term is obtained by concatenating the previous two terms 2 and 3 to get 23.
%t A104458 nxt[{a_,b_}]:={b,FromDigits[Join[IntegerDigits[a],IntegerDigits[b]]]}; NestList[nxt,{2,3},10][[All,1]] (* _Harvey P. Dale_, Jul 23 2018 *)
%K A104458 easy,nonn,base
%O A104458 1,1
%A A104458 _Parthasarathy Nambi_, Apr 21 2005
%E A104458 More terms from _Harvey P. Dale_, Jul 23 2018