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A235497
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2n concatenated with n.
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6
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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
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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a(n) = 2*n*10^floor(log_10(n) + 1) + n.
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MATHEMATICA
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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 *)
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PROG
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(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 */
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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STATUS
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approved
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