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7^n concatenated with itself.
1

%I #8 Sep 08 2022 08:46:01

%S 11,77,4949,343343,24012401,1680716807,117649117649,823543823543,

%T 57648015764801,4035360740353607,282475249282475249,

%U 19773267431977326743,1384128720113841287201,9688901040796889010407,678223072849678223072849

%N 7^n concatenated with itself.

%H Vincenzo Librandi, <a href="/A206529/b206529.txt">Table of n, a(n) for n = 0..200</a>

%F a(n) = A020338(7^n).

%e a(1)=77 because 7^1 concatenated with 7^1 is 77.

%t Table[FromDigits[Join[IntegerDigits[7^n],IntegerDigits[7^n]]],{n,0,20}]

%t #*10^IntegerLength[#]+#&/@(7^Range[0,20]) (* _Harvey P. Dale_, Jul 19 2022 *)

%o (Magma) [Seqint(Intseq(7^n) cat Intseq(7^n)): n in [0..20]];

%Y Cf. A000420, A000351, A178664, A206527, A206528.

%K nonn,base,easy

%O 0,1

%A _Vincenzo Librandi_, Mar 18 2012