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 A019552 a(n) is the concatenation of n and 4n. 9
 14, 28, 312, 416, 520, 624, 728, 832, 936, 1040, 1144, 1248, 1352, 1456, 1560, 1664, 1768, 1872, 1976, 2080, 2184, 2288, 2392, 2496, 25100, 26104, 27108, 28112, 29116, 30120, 31124, 32128, 33132, 34136, 35140, 36144, 37148, 38152, 39156, 40160, 41164 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) is divisible by 4 for n >= 2. - 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. FORMULA a(n) = n*10^floor(log_10(4*n) + 1) + 4*n, with n >= 1. - Paolo P. Lava, Mar 24 2010 MAPLE a:=n->n*10^floor(log10(4*n)+1)+4*n: seq(a(n), n=1..50); # Muniru A Asiru, Jun 23 2018 MATHEMATICA Table[FromDigits[Join[IntegerDigits[n], IntegerDigits[4n]]], {n, 50}] (* Harvey P. Dale, May 11 2011 *) nxt[n_]:=Module[{idn=IntegerDigits[n], idn4=IntegerDigits[4n]}, FromDigits[Join[idn, idn4]]]; Array[nxt, 100] (* Vincenzo Librandi, Feb 04 2014 *) PROG (MAGMA) [Seqint(Intseq(4*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014 (PARI) a(n) = eval(Str(n, 4*n)); \\ Michel Marcus, Sep 21 2015 CROSSREFS Cf. concatenation of n and k*n: A020338 (k=1), A019550 (k=2), A019551 (k=3), this sequence (k=4), A019553 (k=5), A009440 (k=6), A009441 (k=7), A009470 (k=8), A009474 (k=9). Sequence in context: A033847 A067295 A212890 * A325728 A305662 A174070 Adjacent sequences:  A019549 A019550 A019551 * A019553 A019554 A019555 KEYWORD nonn,base,less,easy AUTHOR R. Muller STATUS approved

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Last modified August 17 17:25 EDT 2019. Contains 326059 sequences. (Running on oeis4.)