OFFSET
0,2
COMMENTS
Kekulé numbers for certain benzenoids.
REFERENCES
S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p. 302, P_{11}).
LINKS
FORMULA
a(n) = ((sqrt(13) + 7)*((5 + sqrt(13))/2)^n + (sqrt(13) - 7)*((5 - sqrt(13))/2)^n)/(2*sqrt(13)).
G.f.: (1+z)/(1 - 5z + 3z^2).
MAPLE
a[0]:=1: a[1]:=6: for n from 2 to 26 do a[n]:=5*a[n-1]-3*a[n-2] od: seq(a[n], n=0..26);
MATHEMATICA
LinearRecurrence[{5, -3}, {1, 6}, 30] (* Harvey P. Dale, Dec 03 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Jun 19 2005
STATUS
approved