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 A235497 2n concatenated with n. 6
 21, 42, 63, 84, 105, 126, 147, 168, 189, 2010, 2211, 2412, 2613, 2814, 3015, 3216, 3417, 3618, 3819, 4020, 4221, 4422, 4623, 4824, 5025, 5226, 5427, 5628, 5829, 6030, 6231, 6432, 6633, 6834, 7035, 7236, 7437, 7638, 7839, 8040, 8241, 8442, 8643, 8844, 9045 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are divisible by 3. - Michel Marcus, Sep 21 2015 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = 2*n*10^floor(log_10(n) + 1) + n. MATHEMATICA nxt[n_] := Module[{idn = IntegerDigits[n], idn2 = IntegerDigits[2 n]}, FromDigits[Join[idn2, idn]]]; Array[nxt, 50] (* Librandi *) Table[FromDigits[Join[IntegerDigits[2n], IntegerDigits[n]]], {n, 40}] (* Alonso del Arte, Sep 13 2014 *) PROG (MAGMA) [Seqint(Intseq(n) cat Intseq(2*n)): n in [1..50]]; (Maxima) makelist(2*n*10^floor(log(n)/log(10) + 1) + n, n, 50); /* Bruno Berselli, Feb 06 2014, using the closed form added from Alois P. Heinz on Feb 05 2014 */ (PARI) a(n) = eval(Str(2*n, n)); \\ Michel Marcus, Sep 21 2015 CROSSREFS Cf. A019550. Sequence in context: A089059 A114384 A008603 * A086794 A001682 A180963 Adjacent sequences:  A235494 A235495 A235496 * A235498 A235499 A235500 KEYWORD nonn,base,easy AUTHOR Vincenzo Librandi, Feb 04 2014 STATUS approved

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Last modified October 14 14:31 EDT 2019. Contains 328019 sequences. (Running on oeis4.)