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

1,6

Links

Table of n, a(n) for n=1..15.

Keith M. Briggs, Combinatorial Graph Theory

Example

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)

Crossrefs

Sequence in context: A108475 A328007 A098624 * A153445 A208974 A294196

Adjacent sequences: A116076 A116077 A116078 * A116080 A116081 A116082

Keyword

nonn

Author

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

Extensions

a(14) from Michael Sollami, Jan 29 2012

a(15) from Michael Sollami, Feb 04 2012

Status

approved