A152966 Twice repdigit numbers.

0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 22, 44, 66, 88, 110, 132, 154, 176, 198, 222, 444, 666, 888, 1110, 1332, 1554, 1776, 1998, 2222, 4444, 6666, 8888, 11110, 13332, 15554, 17776, 19998, 22222, 44444, 66666, 88888, 111110, 133332, 155554, 177776, 199998

Offset

0,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,0,0,0,11,0,0,0,0,0,0,0,0,-10).

Formula

a(n) = 2*A010785(n).

G.f.: 2*x*(9*x^8+8*x^7+7*x^6+6*x^5+5*x^4+4*x^3+3*x^2+2*x+1) / ((x-1)*(x^2+x+1)*(x^6+x^3+1)*(10*x^9-1)). - Colin Barker, Sep 18 2013

a(n) = 11*a(n-9) - 10*a(n-18). - Wesley Ivan Hurt, Jan 03 2024

Mathematica

Join[{0}, 2*Flatten[Table[FromDigits[PadRight[{}, n, d]], {n, 5}, {d, 9}]]] (* or *) LinearRecurrence[{0, 0, 0, 0, 0, 0, 0, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0, -10}, {0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 22, 44, 66, 88, 110, 132, 154, 176}, 50] (* Harvey P. Dale, Jun 20 2014 *)
CoefficientList[Series[2 x (9 x^8 + 8 x^7 + 7 x^6 + 6 x^5 + 5 x^4 + 4 x^3 + 3 x^2 + 2 x + 1)/((x - 1) (x^2 + x + 1) (x^6 + x^3 + 1) (10 x^9 - 1)), {x, 0, 40}], x] (* Vincenzo Librandi, Jun 21 2014 *)

Crossrefs

Cf. A010785.

Sequence in context: A276128 A368244 A309239 * A066122 A119766 A030143

Adjacent sequences: A152963 A152964 A152965 * A152967 A152968 A152969

Keyword

base,easy,nonn

Author

Omar E. Pol, Dec 16 2008

Status

approved