OFFSET
0,3
COMMENTS
Form the 6 node graph with matrix A=[1,1,1,1,0,0; 1,1,0,0,1,1; 1,0,0,0,0,0; 1,0,0,0,0,0; 0,1,0,0,0,0; 0,1,0,0,0,0]. Then A099176 counts closed walks of length n at either of the degree 5 vertices.
LINKS
Index entries for linear recurrences with constant coefficients, signature (2,4,-4,-4).
FORMULA
G.f.: (1+x)*(1-2*x)/((1-2x^2)(1-2x-2x^2)).
a(n)=(3+sqrt(3))(1+sqrt(3))^n/12+(3-sqrt(3))(1-sqrt(3))^n/12+2^((n-4)/2)(1+(-1)^n) a(n)=A002605(n)/2+2^((n-4)/2)(1+(-1)^n).
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Oct 02 2004
STATUS
approved