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 A134733 #6 Mar 01 2020 12:01:53
%S A134733 1,23,457,891011,1213141516,171819202122,23242526272930,
%T A134733 3132333435363738,394041424344454647,48495051525354555657,
%U A134733 5859606162636465666768,697071727374757677787980
%N A134733 Concatenation of next n imperfect numbers.
%H A134733 Harvey P. Dale, <a href="/A134733/b134733.txt">Table of n, a(n) for n = 1..200</a>
%t A134733 Module[{nn=120,in,len},in=Select[Range[nn],DivisorSigma[1,#]!=2#&];len= Floor[x/.Last[Solve[(x(x+1))/2==Length[in]]]];FromDigits[Flatten[ IntegerDigits/@ #]]&/@TakeList[in,Range[len]]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Mar 01 2020 *)
%Y A134733 Cf. A053067, A132943, A133013. Imperfect numbers: A132999.
%K A134733 base,easy,nonn
%O A134733 1,2
%A A134733 _Omar E. Pol_, Nov 12 2007