A366953 Expansion of e.g.f. -log(1 - x^2/(1-x)^3).

0, 0, 2, 18, 156, 1560, 18600, 262080, 4284000, 79833600, 1671788160, 38878963200, 994367404800, 27741377664000, 838406080512000, 27287153858764800, 951529253875200000, 35392677532692480000, 1398727294865252352000, 58529661706809925632000, 2585234639710708457472000

Offset: 0

Author

Enrique Navarrete, Oct 29 2023

Keywords

• nonn
• changed

Comments

a(n) is the number of ways to choose two elements from each branch of labeled octopuses with n nodes.

A328055(n) is the corresponding sequence if we choose one element only.

Crossrefs

Cf. A029767, A328055.