A049871 a(n) = Sum{a(k): k=0,1,2,...,n-4,n-2,n-1}; a(n-3) is not a summand; initial terms are 1,3,3.

1, 3, 3, 6, 10, 20, 37, 70, 130, 243, 453, 846, 1579, 2948, 5503, 10273, 19177, 35799, 66828, 124752, 232882, 434735, 811546, 1514962, 2828071, 5279331, 9855246, 18397383, 34343506, 64111097, 119680057, 223413991, 417060391, 778551822, 1453369710, 2713093020

Offset

0,2

Links

Table of n, a(n) for n=0..35.

Index entries for linear recurrences with constant coefficients, signature (2,0,-1,1).

Formula

a(n) = 2*a(n-1) - a(n-3) + a(n-4).

G.f.: (x^3-3*x^2+x+1)/(-x^4+x^3-2*x+1). - Harvey P. Dale, Nov 09 2011

Mathematica

LinearRecurrence[{2, 0, -1, 1}, {1, 3, 3, 6}, 40] (* Harvey P. Dale, Nov 09 2011 *)

Crossrefs

Sequence in context: A031504 A298164 A304265 * A049924 A049926 A298954

Adjacent sequences: A049868 A049869 A049870 * A049872 A049873 A049874

Keyword

nonn,easy

Author

Clark Kimberling

Status

approved