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A115597 Triangle read by rows: let a(n,k) = number of graphs on n nodes with chromatic number k; T(n,k) = a(n,n-k), n >= 2, k=0..n-2. 4
1, 1, 2, 1, 3, 6, 1, 4, 16, 12, 1, 5, 31, 84, 34, 1, 6, 52, 318, 579, 87, 1, 7, 81, 867, 5366, 5721, 302, 1, 8, 118, 2028, 28722, 155291, 87381, 1118, 1, 9, 165, 4251, 115391, 1919895, 7855628, 2104349, 5478 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

2,3

LINKS

Table of n, a(n) for n=2..46.

Keith M. Briggs, Combinatorial Graph Theory

EXAMPLE

Table of values of a(n,k): number of graphs on n nodes with chromatic number k

n. = .1...2...3...4....5....6.....7......8........9.......10

k.----------------------------------------------------------

2....0...1...2...6...12...34....87....302.....1118.....5478... = A076278

3....0...0...1...3...16...84...579...5721....87381..2104349... = A076279

4....0...0...0...1....4...31...318...5366...155291..7855628... = A076280

5....0...0...0...0....1....5....52....867....28722..1919895... = A076281

6....0...0...0...0....0....1.....6.....81.....2028...115391... = A076282

7....0...0...0...0....0....0.....1......7......118.....4251

8....0...0...0...0....0....0.....0......1........8......165

9....0...0...0...0....0....0.....0......0........1........9

10...0...0...0...0....0....0.....0......0........0........1

Triangle begins:

1

1 2

1 3 6

1 4 16 12

1 5 31 84 34

1 6 52 318 579 87

1 7 81 867 5366 5721 302

1 8 118 2028 28722 155291 87381 1118

1 9 165 4251 115391 1919895 7855628 2104349 5478

CROSSREFS

Cf. A076278, A076279, A076280, A076281, A076282.

Cf. A084268 (essentially the same sequence).

Sequence in context: A181511 A115196 A093346 * A325007 A103371 A325015

Adjacent sequences:  A115594 A115595 A115596 * A115598 A115599 A115600

KEYWORD

nonn,tabl

AUTHOR

N. J. A. Sloane, based on email from Keith Briggs, Mar 14 2006

STATUS

approved

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Last modified January 23 19:36 EST 2020. Contains 331175 sequences. (Running on oeis4.)