A346779 Number of Halin graphs on n unlabeled nodes.

0, 0, 0, 1, 1, 2, 2, 4, 6, 13, 22, 50, 106, 252, 589, 1475, 3669, 9435, 24345, 63837, 168234, 447562, 1196390, 3218221, 8694411, 23598318, 64292975, 175820236, 482391019, 1327680919, 3664644419, 10142533143, 28141900501, 78269260312, 218170198957, 609414024190

Offset: 1

Author

Eric W. Weisstein, Aug 03 2021

Keywords

• nonn

Examples

			a(4) = 1 (K_4)
a(5) = 1 (W_5)
a(6) = 2 (3-prism graph, W_6)
a(7) = 2 (W_7 and one other)
a(8) = 4 (W_8 and 3 others)
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..1000
• Peter J. Taylor, Python program
• Eric Weisstein's World of Mathematics, Halin Graph.
• Wikipedia, Halin graph.

Crossrefs

Row sums of A380362.

Antidiagonal sums of A295634.

Cf. A380360.

Programs

PARI

A346779seq(36) \\ See PARI Link in A380362 for program code. - Andrew Howroyd, Jan 26 2025

Python

# See Taylor link

Extensions

a(13) from Eric W. Weisstein, Aug 16 2021

a(14) from Eric W. Weisstein, Sep 29 2021

a(15)-a(24) from Peter J. Taylor, May 20 2023

a(25) onwards from Andrew Howroyd, Jan 25 2025