A361245 Number of noncrossing 2,3 cacti with n nodes.

1, 1, 1, 4, 20, 115, 715, 4683, 31824, 222300, 1586310, 11514030, 84742320, 630946446, 4743789260, 35965715780, 274659794160, 2110810059795, 16312695488265, 126693445737170, 988340783454380, 7740875273884445, 60846920004855985, 479854293574853085

Offset: 0

Author

Andrew Howroyd, Mar 08 2023

Keywords

• nonn

Comments

A 2,3 cactus is a cactus composed of bridges and triangles.

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..500
• Wikipedia, Cactus graph.
• Index entries for sequences related to cacti.

Crossrefs

Cf. A091481, A091485, A091486, A091487, A361242, A361244.

Programs

PARI

seq(n) = Vec(1 + x/(1 - serreverse((sqrt(1 + 4*x + O(x^n)) - 1)*(1 - x)^2/2)))