OFFSET
1,1
REFERENCES
K. Balasubramanian, Recent developments in tree-pruning methods and polynomials for cactus graphs and trees, J. Math. Chemistry, 4 (1990) 89-102.
H. Hosoya, K. Balasubramanian, Exact dimer statistics and characteristic polynomials of cacti lattices, Theor. Chim. Acta 76 (1989) 315-329.
FORMULA
a(n) = (3/2)-3^(n-1)*53+3^(2*n-2)*(64*n^2-148*n)+(97/6)*3^(2*n).
G.f.: 2*x*(5+241*x+495*x^2+27*x^3)/((1-x)*(1-3*x)*(1-9*x)^3). - Bruno Berselli, Dec 30 2012
MAPLE
a := proc (n) options operator, arrow: 3/2-53*3^(n-1)+3^(2*n-2)*(64*n^2-148*n)+(97/6)*3^(2*n) end proc: seq(a(n), n = 1 .. 18);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Emeric Deutsch, Dec 30 2012
EXTENSIONS
Offset changed from 0 to 1 by Bruno Berselli, Dec 30 2012
STATUS
approved