A175237 a(n) = 2*(10^n - 7).

6, 186, 1986, 19986, 199986, 1999986, 19999986, 199999986, 1999999986, 19999999986, 199999999986, 1999999999986, 19999999999986, 199999999999986, 1999999999999986, 19999999999999986, 199999999999999986, 1999999999999999986, 19999999999999999986, 199999999999999999986

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..100

Index entries for linear recurrences with constant coefficients, signature (11,-10).

Formula

G.f.: 6*x*(1 + 20*x)/((1-x)*(1-10*x)). - Vincenzo Librandi, Apr 26 2014

From Elmo R. Oliveira, Dec 04 2025: (Start)

E.g.f.: 2*(6 - 7*exp(x) + exp(10*x)).

a(n) = 11*a(n-1) - 10*a(n-2) for n > 2.

a(n) = 6*A033175(n-1) = A175604(n)/4 = A177112(n)/2. (End)

Mathematica

Join[{6}, Table[FromDigits[Join[{1}, PadLeft[{8, 6}, n, 9]]], {n, 2, 20}]] (* Harvey P. Dale, Mar 22 2012 *)
CoefficientList[Series[6 (1 + 20 x)/((1 - x) (1 - 10 x)), {x, 0, 20}], x] (* Vincenzo Librandi, Apr 26 2014 *)

Prog

(Magma) [2*(10^n-7): n in [1..20]]; // Vincenzo Librandi, Apr 26 2014

Crossrefs

Cf. A033175, A175604, A177112.

Sequence in context: A012181 A012224 A274272 * A222335 A037298 A272467

Adjacent sequences: A175234 A175235 A175236 * A175238 A175239 A175240

Keyword

nonn,easy

Author

Vincenzo Librandi, Nov 15 2010

Status

approved