OFFSET
1,1
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..9999
Eric Weisstein's World of Mathematics, Concatenation
FORMULA
a(n) = n*10^(A004216(n)+1) + n. - Reinhard Zumkeller, Aug 11 2007
G.f.: 11*x/(1-x)^2 - Sum_{d >= 1} 9*x^(10^d)*(100^d*x-10^d*x-100^d)/(1-x)^2). - Robert Israel, Jan 02 2015
a(n) = n || n. (Where "||" denotes "concatenate". See link "Concatenation".) - Halfdan Skjerning, Apr 01 2018
MAPLE
seq(seq((10^d+1)*n, n = 10^(d-1)..10^d-1), d=1..3); # Robert Israel, Jan 02 2015
MATHEMATICA
nxt[n_]:=Module[{idn=IntegerDigits[n], idn1=IntegerDigits[n]}, FromDigits[Join[idn, idn1]]]; Array[nxt, 100] (* Vincenzo Librandi, Feb 04 2014 *)
PROG
(Magma) [Seqint(Intseq(n) cat Intseq(n)): n in [1..46]]; // Bruno Berselli, Mar 20 2013
(Haskell)
a020338 n = read (ns ++ ns) :: Integer where ns = show n
-- Reinhard Zumkeller, Jun 07 2015
(PARI) a(n) = eval(Str(n, n)); \\ Michel Marcus, Sep 10 2015
(Sage) [int(str(n)+str(n)) for n in range(1, 47)] # Danny Rorabaugh, Oct 10 2015
(GAP) Flat(List([1..2], d->List([10^(d-1)..10^d-1], n->(10^d+1)*n))); # Muniru A Asiru, Mar 31 2018
CROSSREFS
KEYWORD
AUTHOR
STATUS
approved