A007855 Infima closed sets in rooted plane trees on n nodes.

1, 3, 13, 63, 326, 1769, 9964, 57843, 344203, 2090470, 12912988, 80899801, 512896540, 3284651548, 21217493460, 138080484819, 904454380446, 5958186674879, 39448465279220, 262359379484522, 1751912981641794, 11741044418866476

Offset: 1

Author

Martin Klazar

Keywords

• nonn

Links

• M. Klazar, Twelve countings with rooted plane trees, European Journal of Combinatorics 18 (1997), 195-210; Addendum, 18 (1997), 739-740.
• Index entries for sequences related to rooted trees

Programs

PARI

my(x='x+O('x^30)); Vec((1/4) * (1+sqrt(1-4*x)) * (1-sqrt(3-2/sqrt(1-4*x)))) \\ Michel Marcus, Apr 05 2019

Formula

G.f.: (1/4) * (1 + sqrt(1-4*x)) * (1 - sqrt(3 - 2 / sqrt(1-4*x))) [from Klazar]. - Sean A. Irvine, Feb 06 2018

Extensions

More terms from Sean A. Irvine, Feb 06 2018