A317975 a(n) = 2*(a(n-1)+a(n-2)+a(n-3))-a(n-4) for n >= 4, with initial terms 0, 1, 1, 0.

0, 1, 1, 0, 4, 9, 25, 76, 216, 625, 1809, 5224, 15100, 43641, 126121, 364500, 1053424, 3044449, 8798625, 25428496, 73489716, 212389225, 613816249, 1773961884, 5126845000, 14816857041, 42821511601, 123756465400, 357662823084, 1033664743129, 2987346551625

Offset

0,5

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)

Formula

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

Mathematica

LinearRecurrence[{2, 2, 2, -1}, {0, 1, 1, 0}, 31] (* Jean-François Alcover, Sep 13 2018 *)

Prog

(PARI) concat([0], Vec((1 - x - 4*x^2)/(1 - 2*x - 2*x^2 - 2*x^3 + x^4) + O(x^40))) \\ Andrew Howroyd, Sep 08 2018

Crossrefs

Sequence in context: A279397 A176497 A304167 * A307396 A028400 A237613

Adjacent sequences: A317972 A317973 A317974 * A317976 A317977 A317978

Keyword

nonn,easy

Author

N. J. A. Sloane, Sep 03 2018

Extensions

Terms a(10) and beyond from Andrew Howroyd, Sep 08 2018

Status

approved