|
Search: id:A052706
|
|
|
| A052706 |
|
A simple context-free grammar. |
|
+0
1
|
|
| 0, 0, 1, 2, 7, 26, 105, 444, 1944, 8734, 40040, 186550, 880750, 4204508, 20260498, 98419392, 481442805, 2369551218, 11725590555, 58303117680, 291151523355
(list; graph; listen)
|
|
|
OFFSET
|
0,4
|
|
|
REFERENCES
|
N. S. S. Gu, N. Y. Li and T. Mansour, 2-Binary trees: bijections and related issues, Discr. Math., 308 (2008), 1209-1221.
|
|
LINKS
|
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 661
|
|
FORMULA
|
G.f.: RootOf(-_Z+_Z^2+_Z^3+x)^2
Recurrence: {a(1) = 0, a(2) = 1, a(3) = 2, (6-27*n+27*n^2)*a(n)+(6+65*n+49*n^2)*a(n+1)+(67*n+66+17*n^2)*a(n+2)+(-5*n^2-25*n-30)*a(n+3)}
|
|
MAPLE
|
spec := [S, {C = Union(S, B, Z), B = Prod(S, C), S = Prod(C, C)}, unlabeled]: seq(combstruct[count](spec, size = n), n = 0..20);
|
|
CROSSREFS
|
Sequence in context: A150554 A150555 A151297 this_sequence A150556 A150557 A150558
Adjacent sequences: A052703 A052704 A052705 this_sequence A052707 A052708 A052709
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
|
|
|
Search completed in 0.002 seconds
|
