OFFSET
0,2
COMMENTS
Let G_n be the graph with vertices {(a,b) : 1<=a<=9, 1<=b<=2n-1, a+b odd} and edges between (a,b) and (c,d) if and only if |a-b|=|c-d|=1. Then a(n) is the number of independent sets in G_n.
LINKS
Z. Zhang, Merrifield-Simmons index of generalized Aztec diamond and related graphs, MATCH Commun. Math. Comput. Chem. 56 (2006) 625-636.
FORMULA
G.f: (1 - 58*x + 799*x^2 - 4041*x^3 + 8286*x^4 - 7357*x^5 + 2660*x^6 - 312*x^7)/(1 - 74*x + 1450*x^2 - 10672*x^3 + 34214*x^4 - 50814*x^5 + 34671*x^6 - 9772*x^7 + 936*x^8).
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Steve Butler, Jan 25 2015
STATUS
approved