A026385 Sum{T(n-k,k)}, 0<=k<=[ n/2 ], where T is the array in A026374.

1, 1, 2, 4, 6, 11, 20, 33, 59, 104, 178, 314, 549, 952, 1669, 2913, 5074, 8872, 15482, 27007, 47172, 82325, 143675, 250848, 437822, 764198, 1334041, 2328512, 4064457, 7094833, 12384034, 21616716, 37732990, 65863651

Offset

0,3

Links

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

Index entries for linear recurrences with constant coefficients, signature (0,1,3,1).

Formula

G.f.: (1+x+x^2)/(1-x^2-3x^3-x^4). - Ralf Stephan, Apr 30 2004

a(n) = a(n-2) + 3*a(n-3) + a(n-4) for n>3. - Vincenzo Librandi, Jun 19 2014

Mathematica

LinearRecurrence[{0, 1, 3, 1}, {1, 1, 2, 4}, 40] (* Harvey P. Dale, Jun 18 2014 *)
CoefficientList[Series[(1 + x + x^2)/(1 - x^2 - 3 x^3 - x^4), {x, 0, 40}], x] (* Vincenzo Librandi, Jun 19 2014 *)

Prog

(Magma) I:=[1, 1, 2, 4]; [n le 4 select I[n] else Self(n-2)+3*Self(n-3)+Self(n-4): n in [1..40]]; // Vincenzo Librandi, Jun 19 2014

Crossrefs

Sequence in context: A113913 A002097 A026757 * A254532 A199926 A068330

Adjacent sequences: A026382 A026383 A026384 * A026386 A026387 A026388

Keyword

nonn

Author

Clark Kimberling

Status

approved