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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.

%I A126736 #3 Mar 30 2012 16:50:37
%S A126736 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,
%T A126736 5036,182,1,7,110,1940,27794,149551,80947,730,1,8,156,4125,113272,
%U A126736 1890221,7694428,2010328,4032
%N 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.
%H A126736 Keith M. Briggs, <a href="http://keithbriggs.info/cgt.html">Combinatorial Graph Theory</a>
%e A126736 Array giving number of connected graphs on n nodes with chromatic number k begins:
%e A126736 n=...1...2...3...4....5....6.....7......8........9........10
%e A126736 k.------------------------------------------------------------
%e A126736 2|...0...1...1...3....5...17....44....182......730......4032
%e A126736 3|...0...0...1...2...12...64...475...5036....80947...2010328
%e A126736 4|...0...0...0...1....3...26...282...5009...149551...7694428
%e A126736 5|...0...0...0...0....1....4....46....809....27794...1890221
%e A126736 6|...0...0...0...0....0....1.....5.....74.....1940....113272
%e A126736 7|...0...0...0...0....0....0.....1......6......110......4125
%e A126736 8|...0...0...0...0....0....0.....0......1........7.......156
%Y A126736 First row of array is A005142.
%K A126736 nonn,tabl
%O A126736 0,5
%A A126736 _N. J. A. Sloane_, Feb 16 2007