OFFSET
0,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Z. Skupien, Sparse Hamiltonian 2-decompositions together with exact count of numerous Hamiltonian cycles, Discr. Math., 309 (2009), 6382-6390.
Index entries for linear recurrences with constant coefficients, signature (2,-1,1,-1).
FORMULA
G.f.: (7-6*x-5*x^3)/(1-2*x+x^2-x^3+x^4). - Colin Barker, Dec 30 2011
a(n) = a(n-1) + a(n-3) - 4 for n>2. - Greg Dresden, Feb 09 2020
MATHEMATICA
CoefficientList[Series[(7 - 6*x - 5*x^3)/(1 - 2*x + x^2 - x^3 + x^4), {x, 0, 50}], x] (* G. C. Greubel, Apr 26 2017 *)
LinearRecurrence[{2, -1, 1, -1}, {7, 8, 9, 12}, 40] (* Harvey P. Dale, Aug 07 2021 *)
PROG
(PARI) x='x+O('x^50); Vec((7 - 6*x - 5*x^3)/(1 - 2*x + x^2 - x^3 + x^4)) \\ G. C. Greubel, Apr 26 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Feb 10 2010
STATUS
approved