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
KEYWORD
nonn,base,easy
AUTHOR
Vincenzo Librandi, Feb 04 2014
STATUS
approved