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%I #9 Nov 28 2018 12:20:48
%S 0,0,0,5832,1228800,384375000,153080202240,77461492681776,
%T 48745516577587200,37439062705187626320,34519165560000000000000,
%U 37661140521028611405206520,48018043198541202818460549120,70773783408692477397888505288296,119443378434420330312430518726819840
%N Chromatic polynomial pi_n(z) of the helm graph H_n evaluated at z=n.
%C The helm graph H_n is the graph obtained from an n-wheel graph by adjoining a pendant edge at each node of the cycle.
%H J. A. Gallian, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/DS6">A dynamic survey of graph labeling</a>, Elec. J. Combin., (2013), #DS6.
%H Eric W. Weisstein, <a href="http://mathworld.wolfram.com/HelmGraph.html">Helm Graph</a>
%F Pi_n(z) = z*((1-z)^n*(z-2)+(z-2)^n*(z-1)^n); a(n) = Pi_n(n).
%e a(3) = 3 * ((1 - 3)^3 * (3 - 2) + (3 - 2)^3 * (3 - 1)^3) = 0.
%p P := proc(n,z) z*((1-z)^n*(z-2)+(z-2)^n*(z-1)^n) ; end: A147859 := proc(n) P(n,n) ; end: for n from 1 to 15 do printf("%d,",A147859(n)) ; od: # _R. J. Mathar_, Jan 22 2009
%K easy,nonn
%O 1,4
%A _Jonathan Vos Post_, Nov 16 2008
%E Corrected parentheses, definition and values _R. J. Mathar_, Jan 22 2009
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