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 A113526 #9 May 15 2017 15:24:55
%S A113526 1,3,13,313,13313,31313313,1331331313313,313133131331331313313,
%T A113526 1331331313313313133131331331313313,
%U A113526 3131331313313313133131331331313313313133131331331313313
%N A113526 Define the first two terms to be 1 and 3. All the other terms are obtained by concatenating the two previous terms.
%H A113526 Harvey P. Dale, <a href="/A113526/b113526.txt">Table of n, a(n) for n = 1..16</a>
%e A113526 The third term is 13 which is obtained by concatenating the two previous terms 1 and 3.
%t A113526 a[1] = 1; a[2] = 3; a[n_] := FromDigits@ Join[IntegerDigits@a[n - 2], IntegerDigits@a[n - 1]]; Array[a, 10] (* _Robert G. Wilson v_ *)
%t A113526 nxt[{a_,b_}]:={b,FromDigits[Join[Flatten[IntegerDigits/@{a,b}]]]}; NestList[nxt,{1,3},10][[All,1]] (* _Harvey P. Dale_, May 15 2017 *)
%Y A113526 Cf. A008352.
%K A113526 base,nonn
%O A113526 1,2
%A A113526 _Parthasarathy Nambi_, Jan 12 2006
%E A113526 More terms from _Robert G. Wilson v_, Jan 18 2006