OFFSET
1,1
COMMENTS
Concatenation of digits of n and 2*n. - Harvey P. Dale, Sep 13 2011
All terms are divisible by 6. - Robert Israel, 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
From Robert Israel, Sep 21 2015 (Start)
G.f.: (6*(2*x+75*x^5-60*x^6) + 90*Sum_{k>=1} 10^k*x^(5*10^k)*(5*10^k - (5*10^k-1)*x))/(1-x)^2.
a(n+2) - 2*a(n+1) + a(n) = 45*10^(2*k+1) if n = 5*10^k-2, 90*10^k-450*10^(2*k) if n = 5*10^k-1, 0 otherwise. (End)
MAPLE
seq(n*(10^(1+ilog10(2*n))+2), n=1..100); # Robert Israel, Sep 21 2015
MATHEMATICA
nxt[n_]:=Module[{idn=IntegerDigits[n], idn2=IntegerDigits[2n]}, FromDigits[ Join[ idn, idn2]]]; Array[nxt, 40] (* Harvey P. Dale, Sep 13 2011 *)
PROG
(Magma) [Seqint(Intseq(2*n) cat Intseq(n)): n in [1..50]]; // Vincenzo Librandi, Feb 04 2014
(PARI) a(n) = eval(Str(n, 2*n)); \\ Michel Marcus, Sep 21 2015
(Python)
def a(n): return int(str(n) + str(2*n))
print([a(n) for n in range(1, 46)]) # Michael S. Branicky, Dec 24 2021
CROSSREFS
KEYWORD
nonn,base,less,easy
AUTHOR
R. Muller
EXTENSIONS
Offset changed from 0 to 1 by Vincenzo Librandi, Feb 04 2014
STATUS
approved