A170948 Number of twins with n edges.

0, 0, 0, 11, 226, 3597, 55006, 892791, 15763270, 305360481, 6483720916, 150200835113, 3774756521566, 102339496556342, 2977913930684928, 92579209306356230, 3062597993515937128, 107418845568842941190

Offset

1,4

Links

Table of n, a(n) for n=1..18.

Antonio Breda d'Azevedo, Alexander Mednykh, and Roman Nedela, Enumeration of maps regardless of genus: Geometric approach, Discrete Mathematics, Volume 310, 2010, Pages 1184-1203.

Formula

a(n) = (A170946(n) - A170947(n)) / 2. [Breda d'Azevedo, Mednykh & Nedela, Corollary 4.8] - Andrey Zabolotskiy, Jun 06 2024

Crossrefs

Cf. A170946, A170947, A214816.

Sequence in context: A281257 A187646 A347482 * A245076 A120850 A289716

Adjacent sequences: A170945 A170946 A170947 * A170949 A170950 A170951

Keyword

nonn

Author

N. J. A. Sloane, Feb 21 2010

Status

approved