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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.

%I A317973 #19 Nov 06 2018 11:41:21
%S A317973 -1,2,3,6,23,62,179,522,1503,4346,12563,36302,104919,303222,876323,
%T A317973 2532626,7319423,21153522,61134819,176682902,510623063,1475728046,
%U A317973 4264933203,12325885722,35622470879,102950851562,297533483123,859887725406,2485121649303,7182134864102
%N 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.
%H A317973 Andrew Howroyd, <a href="/A317973/b317973.txt">Table of n, a(n) for n = 0..1000</a>
%H A317973 H. S. M. Coxeter, <a href="http://gdz.sub.uni-goettingen.de/dms/resolveppn/?PPN=GDZPPN002022109">Loxodromic sequences of tangent spheres</a>, Aequationes Mathematicae, 1.1-2 (1968): 104-121. See p. 112.
%H A317973 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,2,2,-1)
%F A317973 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
%t A317973 LinearRecurrence[{2, 2, 2, -1}, {-1, 2, 3, 6}, 30] (* _Jean-François Alcover_, Sep 13 2018 *)
%o A317973 (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
%K A317973 sign,easy
%O A317973 0,2
%A A317973 _N. J. A. Sloane_, Sep 03 2018
%E A317973 Terms a(8) and beyond from _Andrew Howroyd_, Sep 08 2018