A130781 Sequence is identical to its third differences: a(n+3) = 3*a(n+2) - 3*a(n+1) + 2*a(n), with a(0)=a(1)=1, a(2)=2.

1, 1, 2, 5, 11, 22, 43, 85, 170, 341, 683, 1366, 2731, 5461, 10922, 21845, 43691, 87382, 174763, 349525, 699050, 1398101, 2796203, 5592406, 11184811, 22369621, 44739242, 89478485, 178956971, 357913942, 715827883, 1431655765, 2863311530

Offset

0,3

Comments

The inverse binomial transform is 1,0,1,... repeated with period 3, essentially A011655. - R. J. Mathar, Aug 28 2023

Links

Table of n, a(n) for n=0..32.

Index entries for linear recurrences with constant coefficients, signature (3,-3,2).

Formula

3*a(n) = 2^(n+1) + A087204(n+1).

Also first differences of A024494.

G.f.: (1-2x+2x^2)/(1-3x+3x^2-2x^3).

Binomial transform of [1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 0, ...]; i.e., ones in positions 2, 5, 8, 11, ... and the rest zeros. [Corrected by Gary W. Adamson, Jan 07 2008]

Mathematica

a[n_] := a[n] = 3 a[n - 1] - 3 a[n - 2] + 2 a[n - 3]; a[0] = a[1] = 1; a[2] = 2; Table[a@n, {n, 0, 33}] (* Or *)
CoefficientList[ Series[(1 - 2 x + 2 x^2)/(1 - 3 x + 3 x^2 - 2 x^3), {x, 0, 33}], x] (* Robert G. Wilson v, Sep 08 2007 *)
LinearRecurrence[{3, -3, 2}, {1, 1, 2}, 40] (* Harvey P. Dale, Sep 17 2013 *)

Crossrefs

See A130750, A130752, A130755, A129339.

Essentially a duplicate of A024493.

Sequence in context: A309950 A129715 A024493 * A352045 A351970 A071015

Adjacent sequences: A130778 A130779 A130780 * A130782 A130783 A130784

Keyword

nonn,easy

Author

Paul Curtz, Jul 14 2007, Jul 18 2007

Extensions

Edited by N. J. A. Sloane, Jul 28 2007

Status

approved