A246880 a(n) = 6*((10^n-1)/9)*(10^(n+1))+9*(10^n-1)/9.

0, 609, 66099, 6660999, 666609999, 66666099999, 6666660999999, 666666609999999, 66666666099999999, 6666666660999999999, 666666666609999999999, 66666666666099999999999, 6666666666660999999999999, 666666666666609999999999999, 66666666666666099999999999999

Offset

0,2

Comments

Numbers of the form 6...609...9 (i.e., consisting of an odd number of digits with the middle digit 0, all digits to the left of the middle digit 6 and all digits to the right of the middle digit 9).

Links

Table of n, a(n) for n=0..14.

Index entries for linear recurrences with constant coefficients, signature (111,-1110,1000).

Formula

G.f.: 20/(3-300*x)+1/(x-1)+17/(30*x-3); a(n) = 111*a(n-1)-1110*a(n-2)+1000*a(n-3). - Wesley Ivan Hurt, Sep 15 2014

Maple

A246880:=n->(6*((10^n - 1)/9))*(10^(n + 1)) + (9*(10^n - 1)/9): seq(A246880(n), n=0..15); # Wesley Ivan Hurt, Sep 15 2014

Mathematica

Table[(6*((10^n - 1)/9))*(10^(n + 1)) + (9*(10^n - 1)/9), {n, 15}] (* Wesley Ivan Hurt, Sep 15 2014 *)
Join[{0}, CoefficientList[Series[20/(3 x - 300 x^2) + 1/(x^2 - x) + 17/(30 x^2 - 3 x), {x, 0, 30}], x]] (* Wesley Ivan Hurt, Sep 15 2014 *)

Prog

(PARI) a(n)=6*((10^n-1)/9)*(10^(n+1))+9*(10^n-1)/9
(Magma) [(6*((10^n - 1)/9))*(10^(n + 1)) + (9*(10^n - 1)/9) : n in [0..15]]; // Wesley Ivan Hurt, Sep 15 2014

Crossrefs

Subsequence of A001743, A039434, A111065, A111156, A153806, A169731 and A227793.

Sequence in context: A187421 A296825 A186213 * A027514 A246881 A263393

Adjacent sequences: A246877 A246878 A246879 * A246881 A246882 A246883

Keyword

nonn,base,easy

Author

Felix Fröhlich, Sep 06 2014

Status

approved