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

1,6

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.

Example

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)

Prog

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

Crossrefs

Row sums of A380362.

Antidiagonal sums of A295634.

Cf. A380360.

Sequence in context: A268175 A363578 A209025 * A153955 A074028 A181926

Adjacent sequences: A346776 A346777 A346778 * A346780 A346781 A346782

Keyword

nonn

Author

Eric W. Weisstein, Aug 03 2021

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

Status

approved