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 A134794 #7 Sep 26 2021 16:50:42
%S A134794 4,68,91012,14151618,2021222425,262728303233,34353638394042,
%T A134794 4445464849505152,545556575860626364,65666869707274757677,
%U A134794 7880818284858687889091
%N A134794 Concatenation of next n composite numbers.
%H A134794 Harvey P. Dale, <a href="/A134794/b134794.txt">Table of n, a(n) for n = 1..200</a>
%t A134794 cc[x_]:=FromDigits[Flatten[IntegerDigits/@x]]; Module[{nn= 100,cmps,tr,len},cmps = Select[Range[nn],CompositeQ];len=Length[cmps];tr = Floor[ (Sqrt[1+8 len]-1)/2];cc/@TakeList[cmps,Range[tr]]] (* _Harvey P. Dale_, Sep 26 2021 *)
%Y A134794 Cf. A053067, A133013. Composite numbers: A002808.
%K A134794 base,easy,nonn
%O A134794 1,1
%A A134794 _Omar E. Pol_, Nov 26 2007