%I #6 Mar 01 2020 12:01:53
%S 1,23,457,891011,1213141516,171819202122,23242526272930,
%T 3132333435363738,394041424344454647,48495051525354555657,
%U 5859606162636465666768,697071727374757677787980
%N Concatenation of next n imperfect numbers.
%H Harvey P. Dale, <a href="/A134733/b134733.txt">Table of n, a(n) for n = 1..200</a>
%t 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 Cf. A053067, A132943, A133013. Imperfect numbers: A132999.
%K base,easy,nonn
%O 1,2
%A _Omar E. Pol_, Nov 12 2007