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2^n concatenated with itself.
4

%I #22 Aug 29 2024 12:58:13

%S 11,22,44,88,1616,3232,6464,128128,256256,512512,10241024,20482048,

%T 40964096,81928192,1638416384,3276832768,6553665536,131072131072,

%U 262144262144,524288524288,10485761048576,20971522097152,41943044194304

%N 2^n concatenated with itself.

%C a(1)=22 because 2^1 concatenated with 2^1 is 22.

%H Vincenzo Librandi, <a href="/A178664/b178664.txt">Table of n, a(n) for n = 0..200</a>

%F a(n) = A020338(2^n). - _Bruno Berselli_, Mar 14 2012

%t Table[FromDigits[Join[IntegerDigits[2^n],IntegerDigits[2^n]]],{n,0,30}] (* _Vincenzo Librandi_, Mar 14 2012 *)

%t #*10^IntegerLength[#]+#&/@(2^Range[0,25]) (* _Harvey P. Dale_, Aug 29 2024 *)

%o (Magma) [Seqint(Intseq(2^n) cat Intseq(2^n)): n in [0..40]]; // _Vincenzo Librandi_, Mar 14 2012

%Y Cf. A000079.

%K nonn,easy,base

%O 0,1

%A _Vincenzo Librandi_, Jul 10 2010