A317973 a(n) = 2*(a(n-1)+a(n-2)+a(n-3))-a(n-4) for n >= 4, with initial terms -1, 2, 3, 6.

-1, 2, 3, 6, 23, 62, 179, 522, 1503, 4346, 12563, 36302, 104919, 303222, 876323, 2532626, 7319423, 21153522, 61134819, 176682902, 510623063, 1475728046, 4264933203, 12325885722, 35622470879, 102950851562, 297533483123, 859887725406, 2485121649303, 7182134864102

Offset: 0

Author

N. J. A. Sloane, Sep 03 2018

Keywords

• sign
• easy

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..1000
• H. S. M. Coxeter, Loxodromic sequences of tangent spheres, Aequationes Mathematicae, 1.1-2 (1968): 104-121. See p. 112.
• Index entries for linear recurrences with constant coefficients, signature (2,2,2,-1)

Programs

Mathematica

LinearRecurrence[{2, 2, 2, -1}, {-1, 2, 3, 6}, 30] (* Jean-François Alcover, Sep 13 2018 *)

PARI

Vec((-1 + 4*x + x^2 - 2*x^3)/(1 - 2*x - 2*x^2 - 2*x^3 + x^4) + O(x^40)) \\ Andrew Howroyd, Sep 08 2018

Formula

G.f.: (-1 + 4*x + x^2 - 2*x^3)/(1 - 2*x - 2*x^2 - 2*x^3 + x^4). - Andrew Howroyd, Sep 08 2018

Extensions

Terms a(8) and beyond from Andrew Howroyd, Sep 08 2018