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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 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 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 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 June 23 08:04 EDT 2024. Contains 373629 sequences. (Running on oeis4.)