A126736 Triangle read by rows: T(n,k) (n>=2, k=2..n) gives number of connected graphs on n nodes with chromatic number n-k+1.

1, 1, 1, 1, 2, 3, 1, 3, 12, 5, 1, 4, 26, 64, 17, 1, 5, 46, 282, 475, 44, 1, 6, 74, 809, 5009, 5036, 182, 1, 7, 110, 1940, 27794, 149551, 80947, 730, 1, 8, 156, 4125, 113272, 1890221, 7694428, 2010328, 4032

Offset

0,5

Links

Table of n, a(n) for n=0..44.

Keith M. Briggs, Combinatorial Graph Theory

Example

Array giving number of connected graphs on n nodes with chromatic number k begins:
n=...1...2...3...4....5....6.....7......8........9........10
k.------------------------------------------------------------
2|...0...1...1...3....5...17....44....182......730......4032
3|...0...0...1...2...12...64...475...5036....80947...2010328
4|...0...0...0...1....3...26...282...5009...149551...7694428
5|...0...0...0...0....1....4....46....809....27794...1890221
6|...0...0...0...0....0....1.....5.....74.....1940....113272
7|...0...0...0...0....0....0.....1......6......110......4125
8|...0...0...0...0....0....0.....0......1........7.......156

Crossrefs

First row of array is A005142.

Sequence in context: A065078 A203989 A126744 * A253257 A127412 A304791

Adjacent sequences: A126733 A126734 A126735 * A126737 A126738 A126739

Keyword

nonn,tabl

Author

N. J. A. Sloane, Feb 16 2007

Status

approved