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 A019551 a(n) is the concatenation of n and 3n. 9
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 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(3*n) + 1) + 3*n. - Paolo P. Lava, Mar 24 2010 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 *) PROG (MAGMA) [Seqint(Intseq(3*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014 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). Sequence in context: A033025 A044838 A033010 * A098961 A033897 A005029 Adjacent sequences:  A019548 A019549 A019550 * A019552 A019553 A019554 KEYWORD nonn,base,less,easy AUTHOR R. Muller STATUS approved

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Last modified October 18 03:19 EDT 2019. Contains 328135 sequences. (Running on oeis4.)