A317976 a(n) = 2*(a(n-1)+a(n-2)+a(n-3))-a(n-4) for n >= 4, with initial terms 0,0,1,0.

0, 0, 1, 0, 2, 6, 15, 46, 132, 380, 1101, 3180, 9190, 26562, 76763, 221850, 641160, 1852984, 5355225, 15476888, 44729034, 129269310, 373595239, 1079710278, 3120420620, 9018182964, 26063032485, 75323561860, 217689133998, 629133273722, 1818228906675, 5254779066930, 15186593360656, 43890069394800, 126844654738097

Offset: 0

Author

N. J. A. Sloane, Sep 03 2018

Keywords

• nonn
• easy

Links

• Colin Barker, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (2,2,2,-1).

Crossrefs

Other sequences with this recurrence but different initial conditions: A192234, A192237, A317973, A317974, A317975.

Programs

Mathematica

(See A192235.)

PARI

concat(vector(2), Vec(x^2*(1 - 2*x) / (1 - 2*x - 2*x^2 - 2*x^3 + x^4) + O(x^40))) \\ Colin Barker, Sep 09 2018

Formula

G.f.: x^2*(1 - 2*x) / (1 - 2*x - 2*x^2 - 2*x^3 + x^4). - Colin Barker, Sep 09 2018