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A019550 a(n) is the concatenation of n and 2n. 12
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, 4182, 4284, 4386, 4488, 4590 (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
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
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
(Python)
def a(n): return int(str(n) + str(2*n))
print([a(n) for n in range(1, 46)]) # Michael S. Branicky, Dec 24 2021
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.
Supersequence of A117304.
Sequence in context: A359434 A358693 A371413 * A117304 A022759 A335540
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 June 23 08:04 EDT 2024. Contains 373629 sequences. (Running on oeis4.)