OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..250
Index entries for linear recurrences with constant coefficients, signature (33,-154,176,-32).
FORMULA
G.f.: (28*x^4-154*x^3+134*x^2-29*x+1)/(32*x^4-176*x^3+154*x^2-33*x+1).
EXAMPLE
For n = 1 the a(1) = 4 forests are 1.2.3, 1-2.3, 1.2-3, 1-2-3.
MAPLE
a:= n-> ceil((Matrix([[112, 4, 1/8, 0]]). Matrix(4, (i, j)-> if i=j-1 then 1 elif j=1 then [33, -154, 176, -32][i] else 0 fi)^n)[1, 3]):
seq(a(n), n=0..20);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Mar 19 2009
EXTENSIONS
a(0) inserted by Alois P. Heinz, Jan 23 2013
STATUS
approved