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 A022508 #11 Dec 17 2021 06:02:22
%S A022508 4,14,1411,211411,21142112,122112142112,122112141112212211,
%T A022508 2122112231141112212211,21221122311421132221221112,
%U A022508 12312211321321121421132221221112
%N A022508 Describe previous term from the right (method A - initial term is 4).
%C A022508 Method A = 'frequency' followed by 'digit'-indication.
%e A022508 The term after 1411 is obtained by saying "two 1's, one 4, one 1", which gives 211411.
%t A022508 A022508[1]:=4;A022508[n_]:=A022508[n]=FromDigits[Flatten[{Length[#],First[#]}&/@Split[Reverse[IntegerDigits[A022508[n-1]]]]]];Map[A022508,Range[15]] (* _Peter J. C. Moses_, Apr 22 2013 *)
%Y A022508 Cf. A022506, A006711, A022482, A022507-A022513.
%K A022508 nonn,base,easy,nice
%O A022508 0,1
%A A022508 _N. J. A. Sloane_
%E A022508 More terms from _Erich Friedman_