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%I #16 Apr 23 2018 14:22:01
%S 1,1,3,72,11423,11187798,65460885384,2247082682913972,
%T 447548280314975144427,513427482871084962707467332
%N Chromatic invariant of the square grid graph G_(n,n).
%C The square grid graph G_(n,n) has n^2 = A000290(n) vertices and 2*n*(n-1) = A046092(n-1) edges. The chromatic invariant equals the absolute value of the first derivative of the chromatic polynomial evaluated at 1.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/ChromaticInvariant.html">Chromatic Invariant</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/GridGraph.html">Grid Graph</a>
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Chromatic_polynomial">Chromatic Polynomial</a>
%F a(n) = |(d/dq P(n,q))_{q=1}| with P(n,q) = Sum_{k=0..n^2} A182368(n,k) * q^(n^2-k).
%t Abs[Table[Derivative[1][ChromaticPolynomial[GridGraph[{n, n}]]][1], {n, 7}]] (* _Eric W. Weisstein_, May 01 2017 *)
%Y Cf. A000290, A046092, A182368 (chromatic polynomial).
%K nonn,more
%O 1,3
%A _Alois P. Heinz_, May 03 2012
%E a(10) from _Andrew Howroyd_, Apr 23 2018
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