A019553 a(n) is the concatenation of n and 5n.

15, 210, 315, 420, 525, 630, 735, 840, 945, 1050, 1155, 1260, 1365, 1470, 1575, 1680, 1785, 1890, 1995, 20100, 21105, 22110, 23115, 24120, 25125, 26130, 27135, 28140, 29145, 30150, 31155, 32160, 33165, 34170, 35175, 36180, 37185, 38190, 39195, 40200

Offset: 1

Author

R. Muller

Keywords

• nonn
• base
• easy
• less

Comments

All terms are divisible by 15. - Michel Marcus, Sep 21 2015

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), A019551 (k=3), A019552 (k=4), this sequence (k=5), A009440 (k=6), A009441 (k=7), A009470 (k=8), A009474 (k=9).

Programs

Magma

[Seqint(Intseq(5*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014

Maple

a:=n->n*10^floor(log10(5*n)+1)+5*n: seq(a(n),n=1..50); # Muniru A Asiru, Jun 23 2018

Mathematica

n5n[n_]:=Module[{n5=5n},n*10^IntegerLength[n5]+n5]; Array[n5n,40] (* Harvey P. Dale, Apr 08 2012 *)
nxt[n_]:=Module[{idn=IntegerDigits[n], idn5=IntegerDigits[5n]}, FromDigits[Join[idn, idn5]]]; Array[nxt, 100] (* Vincenzo Librandi, Feb 04 2014 *)

PARI

a(n) = eval(Str(n, 5*n)); \\ Michel Marcus, Sep 21 2015