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 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. 4
 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 (list; graph; refs; listen; history; text; internal format)
 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 * A028400 A237613 A220444 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

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Last modified March 19 11:29 EDT 2019. Contains 321329 sequences. (Running on oeis4.)