A019551 a(n) is the concatenation of n and 3n.

13, 26, 39, 412, 515, 618, 721, 824, 927, 1030, 1133, 1236, 1339, 1442, 1545, 1648, 1751, 1854, 1957, 2060, 2163, 2266, 2369, 2472, 2575, 2678, 2781, 2884, 2987, 3090, 3193, 3296, 3399, 34102, 35105, 36108

Offset: 1

Author

R. Muller

Keywords

• nonn
• base
• less
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000
• Sylvester Smith, A Set of Conjectures on Smarandache Sequences, Bulletin of Pure and Applied Sciences, (Bombay, India), Vol. 15 E (No. 1), 1996, pp. 101-107.

Crossrefs

Cf. concatenation of n and k*n: A020338 (k=1), A019550 (k=2), this sequence (k=3), A019552 (k=4), A019553 (k=5), A009440 (k=6), A009441 (k=7), A009470 (k=8), A009474 (k=9).

Programs

Magma

[Seqint(Intseq(3*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014

Maple

a:=n->n*10^floor(log10(3*n)+1)+3*n: seq(a(n),n=1..50); # Muniru A Asiru, Jun 23 2018

Mathematica

nxt[n_]:=Module[{idn=IntegerDigits[n], idn3=IntegerDigits[3n]}, FromDigits[Join[idn, idn3]]]; Array[nxt, 100] (* Vincenzo Librandi, Feb 04 2014 *)
Table[n*10^IntegerLength[3n]+3n,{n,40}] (* Harvey P. Dale, Apr 24 2022 *)