OFFSET
1,2
REFERENCES
S. Kitaev, A. Burstein and T. Mansour. Counting independent sets in certain classes of (almost) regular graphs, Pure Mathematics and Applications (PU.M.A.) 19 (2008), no. 2-3, 17-26.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
S. Kitaev, A. Burstein and T. Mansour. Counting independent sets in certain classes of (almost) regular graphs
Index entries for linear recurrences with constant coefficients, signature (3,4,-4).
FORMULA
G.f.:(1+4*x-4*x^2)/(1-3*x-4*x^2+4*x^3)
a(1)=1, a(2)=7, a(3)=21, a(n)=3*a(n-1)+4*a(n-2)-4*a(n-3). - Harvey P. Dale, May 10 2015
MATHEMATICA
CoefficientList[Series[(1+4x-4x^2)/(1-3x-4x^2+4x^3), {x, 0, 20}], x] (* or *) LinearRecurrence[{3, 4, -4}, {1, 7, 21}, 20] (* Harvey P. Dale, May 10 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Signy Olafsdottir (signy06(AT)ru.is), May 07 2010
EXTENSIONS
Definition clarified by Harvey P. Dale, May 10 2015
STATUS
approved