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

1,5

Links

Table of n, a(n) for n=1..28.

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.

Formula

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

Crossrefs

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

Sequence in context: A284998 A009423 A008325 * A123383 A281707 A225172

Adjacent sequences: A004063 A004064 A004065 * A004067 A004068 A004069

Keyword

nonn

Author

Gunnar Brinkmann, Brendan McKay and Eric Rogoyski

Extensions

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

Status

approved