A049875 - OEIS

A049875

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 2,3,3.

2, 3, 3, 6, 11, 22, 41, 77, 143, 267, 498, 930, 1736, 3241, 6050, 11294, 21083, 39357, 73470, 137151, 256028, 477943, 892205, 1665533, 3109151, 5804040, 10834752, 20225886, 37756883, 70483054, 131574974, 245618951, 458511731, 855931542, 1597819107, 2982745434

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OFFSET

0,1

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 - 1)*(-2*x^2 + x + 2)/(x^4 - x^3 + 2*x - 1). - Chai Wah Wu, Feb 20 2023

MATHEMATICA

LinearRecurrence[{2, 0, -1, 1}, {2, 3, 3, 6}, 40] (* Harvey P. Dale, Nov 21 2023 *)

CROSSREFS