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%I #8 Mar 16 2020 22:16:57
%S 1,1,6,20,69,196,554,1368,3240,7110,14896,29624,56755,104468,186484,
%T 322800,544590,896259,1443834,2278640,3531647,5380064,8069672,
%U 11926928,17392983,25042836,35637168,50152068,69853604,96344440,131669538
%N Number of directed loopless multigraphs on 4 nodes with n arcs.
%H Andrew Howroyd, <a href="/A050930/b050930.txt">Table of n, a(n) for n = 0..1000</a>
%F G.f.: (2*x^18 + 9*x^17 + 20*x^16 + 46*x^15 + 98*x^14 + 133*x^13 + 196*x^12 + 226*x^11 + 254*x^10 + 240*x^9 + 207*x^8 + 128*x^7 + 92*x^6 + 43*x^5 + 24*x^4 + 8*x^3 + 2*x^2-x + 1)/((x^4-1)^3*(x^3-1)^4*(x^2-1)^3*(x-1)^2).
%Y Column k=4 of A333361.
%Y Cf. A037240.
%K easy,nonn
%O 0,3
%A _Vladeta Jovovic_, Dec 30 1999
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