A178664 a(n) = 2^n concatenated with itself.

11, 22, 44, 88, 1616, 3232, 6464, 128128, 256256, 512512, 10241024, 20482048, 40964096, 81928192, 1638416384, 3276832768, 6553665536, 131072131072, 262144262144, 524288524288, 10485761048576, 20971522097152, 41943044194304, 83886088388608, 1677721616777216

Offset: 0

Author

Vincenzo Librandi, Jul 10 2010

Keywords

• nonn
• easy
• base

Examples

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

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..200

Crossrefs

Cf. A000079.

Programs

Magma

[Seqint(Intseq(2^n) cat Intseq(2^n)): n in [0..40]]; // Vincenzo Librandi, Mar 14 2012

Maple

a:= n-> parse(cat(2^n$2)):
seq(a(n), n=0..25);  # Alois P. Heinz, Jun 24 2025

Mathematica

Table[FromDigits[Join[IntegerDigits[2^n],IntegerDigits[2^n]]],{n,0,30}] (* Vincenzo Librandi, Mar 14 2012 *)
#*10^IntegerLength[#]+#&/@(2^Range[0,25]) (* Harvey P. Dale, Aug 29 2024 *)

Formula

a(n) = A020338(2^n). - Bruno Berselli, Mar 14 2012