A074581 a(n)=T(3n+1), where T(n) are tribonacci numbers A000073.

0, 2, 13, 81, 504, 3136, 19513, 121415, 755476, 4700770, 29249425, 181997601, 1132436852, 7046319384, 43844049029, 272809183135, 1697490356184, 10562230626642, 65720971788709, 408933139743937, 2544489349890656

Offset

0,2

Links

Table of n, a(n) for n=0..20.

Index entries for linear recurrences with constant coefficients, signature (7,-5,1).

Formula

a(n) = 7a(n-1)-5a(n-2)+a(n-3), a(0)=0, a(1)=2, a(2)=13.

G.f.: (2x-x^2)/(1-7x+5x^2-x^3).

Mathematica

CoefficientList[Series[(2*x-x^2)/(1-7*x+5*x^2-x^3), {x, 0, 40}], x]
LinearRecurrence[{7, -5, 1}, {0, 2, 13}, 30] (* Harvey P. Dale, Jul 22 2021 *)

Crossrefs

Cf. A000073.

Sequence in context: A189087 A037739 A037634 * A020059 A162772 A317892

Adjacent sequences: A074578 A074579 A074580 * A074582 A074583 A074584

Keyword

easy,nonn

Author

Mario Catalani (mario.catalani(AT)unito.it), Aug 24 2002

Extensions

Definition corrected by David Scambler, Oct 18 2010

Status

approved