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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. 7
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 (list; table; graph; refs; listen; history; text; internal format)
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: A203989 A126744 A122078 * A253257 A127412 A304791

Adjacent sequences:  A126733 A126734 A126735 * A126737 A126738 A126739

KEYWORD

nonn,tabl

AUTHOR

N. J. A. Sloane, Feb 16 2007

STATUS

approved

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Last modified September 17 04:49 EDT 2019. Contains 327119 sequences. (Running on oeis4.)