A116079 Number of connected triangle-free graphs on n nodes with chromatic number 3.

0, 0, 0, 0, 1, 2, 15, 85, 650, 5800, 65243, 931258, 17182237, 414512599, 13161989059

Offset: 1

Author

N. J. A. Sloane, based on email from Keith Briggs, Mar 21 2006

Keywords

• nonn

Examples

			Table of number of connected triangle-free graphs on n nodes with chromatic number k begins:
(The first row is the same as the number of connected bipartite graphs on n nodes, A005142)
n=...1...2...3...4...5....6....7.....8.....9.....10......11.......12.........13
k.-----------------------------------------------------------------------------
2|...0...1...1...3...5...17...44...182...730...4032...25598...212780....2241730 (A005142)
3|...0...0...0...0...1....2...15....85...650...5800...65243...931258...17182237 (the present sequence)
4|...0...0...0...0...0....0....0.....0.....0......0.......1.......23.......1085 (A126741)
		

Links

• Keith M. Briggs, Combinatorial Graph Theory

Extensions

a(14) from Michael Sollami, Jan 29 2012

a(15) from Michael Sollami, Feb 04 2012