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A019550 a(n) is the concatenation of n and 2n. 11
12, 24, 36, 48, 510, 612, 714, 816, 918, 1020, 1122, 1224, 1326, 1428, 1530, 1632, 1734, 1836, 1938, 2040, 2142, 2244, 2346, 2448, 2550, 2652, 2754, 2856, 2958, 3060, 3162, 3264, 3366, 3468, 3570, 3672, 3774, 3876, 3978, 4080 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Concatenation of digits of n and 2*n. - Harvey P. Dale, Sep 13 2011

All terms are divisible by 6. - Robert Israel, 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.

FORMULA

a(n) = n * 10^floor(log_10(2*n) + 1) + 2*n. - Paolo P. Lava, Mar 24 2010

From Robert Israel, Sep 21 2015 (Start)

G.f.: (6*(2*x+75*x^5-60*x^6) + 90*Sum_{k>=1} 10^k*x^(5*10^k)*(5*10^k - (5*10^k-1)*x))/(1-x)^2.

a(n+2) - 2*a(n+1) + a(n) = 45*10^(2*k+1) if n = 5*10^k-2, 90*10^k-450*10^(2*k) if n = 5*10^k-1, 0 otherwise. (End)

MAPLE

seq(n*(10^(1+ilog10(2*n))+2), n=1..100); # Robert Israel, Sep 21 2015

MATHEMATICA

nxt[n_]:=Module[{idn=IntegerDigits[n], idn2=IntegerDigits[2n]}, FromDigits[ Join[ idn, idn2]]]; Array[nxt, 40] (* Harvey P. Dale, Sep 13 2011 *)

PROG

(MAGMA) [Seqint(Intseq(2*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014

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

CROSSREFS

Cf. concatenation of n and k*n: A020338 (k=1), this sequence (k=2), A019551 (k=3), A019552 (k=4), A019553 (k=5), A009440 (k=6), A009441 (k=7), A009470 (k=8), A009474 (k=9).

Cf. A235497.

Sequence in context: A140470 A141766 A069056 * A117304 A022759 A091193

Adjacent sequences:  A019547 A019548 A019549 * A019551 A019552 A019553

KEYWORD

nonn,base,less,easy

AUTHOR

R. Muller

EXTENSIONS

Offset changed from 0 to 1 by Vincenzo Librandi, Feb 04 2014

STATUS

approved

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Last modified May 22 15:13 EDT 2019. Contains 323480 sequences. (Running on oeis4.)