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A052283
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Triangle read by rows: T(n,k) is the number of unlabeled directed graphs on n nodes with k arcs, k=0..n*(n-1).
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9
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1, 1, 1, 1, 1, 1, 1, 4, 4, 4, 1, 1, 1, 1, 5, 13, 27, 38, 48, 38, 27, 13, 5, 1, 1, 1, 1, 5, 16, 61, 154, 379, 707, 1155, 1490, 1670, 1490, 1155, 707, 379, 154, 61, 16, 5, 1, 1, 1, 1, 5, 17, 76, 288, 1043, 3242, 8951, 21209, 43863, 78814, 124115, 171024, 207362, 220922, 207362, 171024, 124115, 78814, 43863, 21209, 8951, 3242, 1043, 288, 76, 17, 5, 1, 1
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OFFSET
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0,8
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COMMENTS
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Triangular array read by rows T(n,k) is the number of unlabeled directed graphs (no self loops allowed) on n nodes with exactly k edges where n >= 1, 0 <= k <= n(n-1). - Geoffrey Critzer, Nov 01 2011
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REFERENCES
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F. Harary and E. M. Palmer, Graphical Enumeration, Academic Press, NY, 1973, p. 247.
J. L. Gross and J. Yellen, eds., Handbook of Graph Theory, CRC Press, 2004; p. 522.
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LINKS
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FORMULA
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T(2k,k) = T(2k+1,k) = T(2k+2,k) =... and is the maximum value of column k. - Geoffrey Critzer, Nov 01 2011
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EXAMPLE
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[1],
[1],
[1,1,1],
[1,1,4,4,4,1,1],
[1,1,5,13,27,38,48,38,27,13,5,1,1];
(the last batch giving the numbers of directed graphs with 4 nodes and from 0 to 12 arcs).
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MATHEMATICA
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Table[CoefficientList[GraphPolynomial[n, x, Directed], x], {n, 1, 10}] (* Geoffrey Critzer, Nov 01 2011 *)
permcount[v_] := Module[{m = 1, s = 0, k = 0, t}, For[i = 1, i <= Length[v], i++, t = v[[i]]; k = If[i > 1 && t == v[[i - 1]], k + 1, 1]; m *= t*k; s += t]; s!/m];
edges[v_, t_] := Product[g = GCD[v[[i]], v[[j]]]; t[v[[i]]*v[[j]]/g]^(2 g), {i, 2, Length[v]}, {j, 1, i-1}] * Product[ t[v[[i]]]^(v[[i]] - 1), {i, 1, Length[v]}];
gp[n_] := (s = 0; Do[s += permcount[p]*edges[p, 1 + x^# &], {p, IntegerPartitions[n]}]; s/n!);
A052283 = Reap[For[n = 1, n <= 6, n++, p = gp[n]; For[k = 0, k <= Exponent[p, x], k++, Sow[Coefficient[p, x, k]]]]][[2, 1]] (* Jean-François Alcover, Jul 09 2018, after Andrew Howroyd *)
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PROG
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(PARI)
permcount(v) = {my(m=1, s=0, k=0, t); for(i=1, #v, t=v[i]; k=if(i>1&&t==v[i-1], k+1, 1); m*=t*k; s+=t); s!/m}
edges(v, t) = {prod(i=2, #v, prod(j=1, i-1, my(g=gcd(v[i], v[j])); t(v[i]*v[j]/g)^(2*g))) * prod(i=1, #v, t(v[i])^(v[i]-1))}
gp(n) = {my(s=0); forpart(p=n, s+=permcount(p)*edges(p, i->1+x^i)); s/n!}
for(n=1, 6, my(p=gp(n)); for(k=0, poldegree(p), print1(polcoeff(p, k), ", ")); print); \\ Andrew Howroyd, Nov 05 2017
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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EXTENSIONS
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a(0)=1 prepended and terms a(62) and beyond from Andrew Howroyd, Apr 20 2020
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STATUS
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approved
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