A235497 2n concatenated with n.

21, 42, 63, 84, 105, 126, 147, 168, 189, 2010, 2211, 2412, 2613, 2814, 3015, 3216, 3417, 3618, 3819, 4020, 4221, 4422, 4623, 4824, 5025, 5226, 5427, 5628, 5829, 6030, 6231, 6432, 6633, 6834, 7035, 7236, 7437, 7638, 7839, 8040, 8241, 8442, 8643, 8844, 9045

Offset: 1

Author

Vincenzo Librandi, Feb 04 2014

Keywords

• nonn
• base
• easy

Comments

All terms are divisible by 3. - Michel Marcus, Sep 21 2015

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A019550.

Programs

Magma

[Seqint(Intseq(n) cat Intseq(2*n)): n in [1..50]];

Mathematica

nxt[n_] := Module[{idn = IntegerDigits[n], idn2 = IntegerDigits[2 n]}, FromDigits[Join[idn2, idn]]]; Array[nxt, 50] (* Librandi *)
Table[FromDigits[Join[IntegerDigits[2n], IntegerDigits[n]]], {n, 40}] (* Alonso del Arte, Sep 13 2014 *)

Maxima

makelist(2*n*10^floor(log(n)/log(10) + 1) + n,n,50); /* Bruno Berselli, Feb 06 2014, using the closed form added from Alois P. Heinz on Feb 05 2014 */

PARI

a(n) = eval(Str(2*n, n)); \\ Michel Marcus, Sep 21 2015

Formula

a(n) = 2*n*10^floor(log_10(n) + 1) + n.