A004066 Number of simple regular trivalent bicolored graphs with 2n nodes.

0, 0, 1, 1, 2, 6, 14, 41, 157, 725, 4196, 29817, 246646, 2297088, 23503564, 260265650, 3090341095, 39101587595, 524783295041, 7443251159470, 111222017297268, 1746166043555813, 28734210790531045, 494526547845483641, 8883866458982018870, 166286444108288113541, 3237719185652343485853, 65477290060076644381373

Offset: 1

Author

Gunnar Brinkmann, Brendan McKay and Eric Rogoyski

Keywords

• nonn

Links

• Sean A. Irvine, On the difference between A004066 and A008325
• Patric R. J. Östergård, Classifying generalized Howell designs, Designs Codes Cryptog. (2025). See Sect. 3.2.1.

Crossrefs

Cf. A000512, A000840, A008325 (bipartite), A006823 (connected).

Formula

a(n) = (A000840(n) + A000512(n))/2. - Andrew Howroyd, Apr 01 2020

Extensions

a(1)-a(2) prepended and terms a(15) and beyond from Andrew Howroyd, Apr 01 2020