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 A125058 #9 Jun 05 2021 10:22:52
%S A125058 1,2,212,2122212,21222122122122212,
%T A125058 21222122122122212212221221222122122122212,
%U A125058 212221221221222122122212212221221221222122122212212212221221222122122122212212221221222122122122212
%N A125058 A sequence of words over an alphabet of two letters: a(0) = 1, a(1) = 2; a(n+2) = a(n+1)a(n)a(n+1).
%C A125058 A055642(a(n)) = A001333(n). - _Reinhard Zumkeller_, Feb 02 2007
%D A125058 Suggested by a posting by Igor G. Korepanov to "Jim's Forum", Jan 10 2007.
%F A125058 a(n)=(a(n-1)*A011557(A001333(n-2))+a(n-2))*A011557(A001333(n-2))+a(n-1). - _Reinhard Zumkeller_, Feb 02 2007
%t A125058 nxt[{a_,b_}]:={b,FromDigits[Flatten[Join[IntegerDigits[b],IntegerDigits[a],IntegerDigits[ b]]]]}; NestList[nxt,{1,2},7][[All,1]] (* _Harvey P. Dale_, Jun 05 2021 *)
%K A125058 nonn,base
%O A125058 0,2
%A A125058 _N. J. A. Sloane_, Jan 10 2007