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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.
4
-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
0,2
LINKS
H. S. M. Coxeter, Loxodromic sequences of tangent spheres, Aequationes Mathematicae, 1.1-2 (1968): 104-121. See p. 112.
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
MATHEMATICA
LinearRecurrence[{2, 2, 2, -1}, {-1, 2, 3, 6}, 30] (* Jean-François Alcover, Sep 13 2018 *)
PROG
(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
CROSSREFS
Sequence in context: A261963 A183179 A018300 * A361333 A327013 A171708
KEYWORD
sign,easy
AUTHOR
N. J. A. Sloane, Sep 03 2018
EXTENSIONS
Terms a(8) and beyond from Andrew Howroyd, Sep 08 2018
STATUS
approved