A049870 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 1,2,4.

1, 2, 4, 6, 11, 20, 38, 71, 133, 248, 463, 864, 1613, 3011, 5621, 10493, 19588, 36566, 68260, 127425, 237872, 444050, 828935, 1547423, 2888668, 5392451, 10066414, 18791583, 35079383, 65484803, 122244437, 228201074, 425996728, 795233822, 1484511007, 2771226360

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^3-1)/(x^4-x^3+2*x-1).

Mathematica

LinearRecurrence[{2, 0, -1, 1}, {1, 2, 4, 6}, 40] (* Harvey P. Dale, Mar 23 2015 *)

Crossrefs

Sequence in context: A199926 A068330 A017993 * A093970 A333098 A107428

Adjacent sequences: A049867 A049868 A049869 * A049871 A049872 A049873

Keyword

nonn,easy

Author

Clark Kimberling

Status

approved