A178664 -id:A178664 - cp's OEIS frontend

A206527 3^n concatenated with itself.

11, 33, 99, 2727, 8181, 243243, 729729, 21872187, 65616561, 1968319683, 5904959049, 177147177147, 531441531441, 15943231594323, 47829694782969, 1434890714348907, 4304672143046721, 129140163129140163, 387420489387420489

Offset: 0

Vincenzo Librandi, Mar 14 2012

			a(1)=33 because 3^1 concatenated with 3^1 is 33.

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

Cf. A178664, A000244.

[Seqint(Intseq(3^n) cat Intseq(3^n)): n in [0..18]]; // Bruno Berselli, Mar 14 2012

Table[FromDigits[Join[IntegerDigits[3^n], IntegerDigits[3^n]]], {n, 0, 18}] (* Bruno Berselli, Mar 14 2012 *)
Table[3^n 10^IntegerLength[3^n]+3^n,{n,0,20}] (* Harvey P. Dale, May 27 2019 *)

a(n) = A020338(3^n). - Bruno Berselli, Mar 14 2012

A206528 5^n concatenated with itself.

Original entry on oeis.org

11, 55, 2525, 125125, 625625, 31253125, 1562515625, 7812578125, 390625390625, 19531251953125, 97656259765625, 4882812548828125, 244140625244140625, 12207031251220703125, 61035156256103515625, 3051757812530517578125, 152587890625152587890625

Offset: 0

Vincenzo Librandi, Mar 17 2012

			a(1)=55 because 5^1 concatenated with 5^1 is 55.

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

Cf. A000351, A178664, A206527.

[Seqint(Intseq(5^n) cat Intseq(5^n)): n in [0..20]];

Table[FromDigits[Join[IntegerDigits[5^n],IntegerDigits[5^n]]],{n,0,20}]

a(n) = A020338(5^n).

A381259 Numbers obtained by concatenating powers of 2, sorted into increasing order.

Original entry on oeis.org

1, 2, 4, 8, 11, 12, 14, 16, 18, 21, 22, 24, 28, 32, 41, 42, 44, 48, 64, 81, 82, 84, 88, 111, 112, 114, 116, 118, 121, 122, 124, 128, 132, 141, 142, 144, 148, 161, 162, 164, 168, 181, 182, 184, 188, 211, 212, 214, 216, 218, 221, 222, 224, 228, 232, 241, 242, 244, 248, 256, 264

Offset: 1

Stefano Spezia, Feb 18 2025

Take the list {2^i: i >= 0} and concatenate its terms (allowing multiple copies) in any order; then sort the result into increasing order.

The term a(32) = 128 is a power of 2 as well as the concatenation of several powers of 2. - Rémy Sigrist, Feb 20 2025

			11 is a term because it is the concatenation of 1 = 2^0 with itself;
12 is a term because it is the concatenation of 1 = 2^0 with 2 = 2^1;
32 is a term because it is equal to 2^5;
168 is a term because it is the concatenation of 16 = 2^4 with 8 = 2^3.
0 is not a term because it is not a power of 2.

Rémy Sigrist, Table of n, a(n) for n = 1..11921
Rémy Sigrist, PARI program

Supersequence of A028846.
Some subsequences: A000079, A045507, A178664.
Cf. A152242.

PARI
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A206529 7^n concatenated with itself.

Original entry on oeis.org

11, 77, 4949, 343343, 24012401, 1680716807, 117649117649, 823543823543, 57648015764801, 4035360740353607, 282475249282475249, 19773267431977326743, 1384128720113841287201, 9688901040796889010407, 678223072849678223072849

Offset: 0

Vincenzo Librandi, Mar 18 2012

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

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

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

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

Table[FromDigits[Join[IntegerDigits[7^n],IntegerDigits[7^n]]],{n,0,20}]
#*10^IntegerLength[#]+#&/@(7^Range[0,20]) (* Harvey P. Dale, Jul 19 2022 *)

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

cp's OEIS Frontend

A206527 3^n concatenated with itself.

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A206528 5^n concatenated with itself.

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A381259 Numbers obtained by concatenating powers of 2, sorted into increasing order.

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PARI

A206529 7^n concatenated with itself.

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Magma

Mathematica

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