A115597 - OEIS

%I #10 Oct 16 2016 02:23:24

%S 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,

%T 5721,302,1,8,118,2028,28722,155291,87381,1118,1,9,165,4251,115391,

%U 1919895,7855628,2104349,5478

%N 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.

%H Keith M. Briggs, <a href="http://keithbriggs.info/cgt.html">Combinatorial Graph Theory</a>

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

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

%e k.----------------------------------------------------------

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

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

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

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

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

%e 7....0...0...0...0....0....0.....1......7......118.....4251

%e 8....0...0...0...0....0....0.....0......1........8......165

%e 9....0...0...0...0....0....0.....0......0........1........9

%e 10...0...0...0...0....0....0.....0......0........0........1

%e Triangle begins:

%e 1

%e 1 2

%e 1 3 6

%e 1 4 16 12

%e 1 5 31 84 34

%e 1 6 52 318 579 87

%e 1 7 81 867 5366 5721 302

%e 1 8 118 2028 28722 155291 87381 1118

%e 1 9 165 4251 115391 1919895 7855628 2104349 5478

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

%Y Cf. A084268 (essentially the same sequence).

%K nonn,tabl

%O 2,3

%A _N. J. A. Sloane_, based on email from _Keith Briggs_, Mar 14 2006