OFFSET
0,2
COMMENTS
Counts closed walks of length 2n at any node of degree 4 on the Herschel graph. With interpolated zeros, counts closed walks of length n. The g.f. is then (1-9x^2+2x^4)/((1-2x^2)(1-11x^2))=(1-14x^2+53x^4-64x^6+12x^8)/((1-2x^2)^2(1-3x^2)(1-11x^2)). Binomial transform of A099913.
LINKS
Eric Weisstein's World of Mathematics, Herschel Graph
FORMULA
G.f. : (1-9x+2x^2)/((1-2x)(1-11x)); a(n)=0^n/11+811^(n-1)/3+2^(n+1)/3.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Oct 30 2004
STATUS
approved