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Concatenation of next n composite numbers.
1

%I #7 Sep 26 2021 16:50:42

%S 4,68,91012,14151618,2021222425,262728303233,34353638394042,

%T 4445464849505152,545556575860626364,65666869707274757677,

%U 7880818284858687889091

%N Concatenation of next n composite numbers.

%H Harvey P. Dale, <a href="/A134794/b134794.txt">Table of n, a(n) for n = 1..200</a>

%t 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 Cf. A053067, A133013. Composite numbers: A002808.

%K base,easy,nonn

%O 1,1

%A _Omar E. Pol_, Nov 26 2007