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A049297
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Number of nonisomorphic circulant digraphs (i.e., Cayley digraphs for the cyclic group) of order n.
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12
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1, 2, 3, 6, 6, 20, 14, 46, 51, 140, 108, 624, 352, 1400, 2172, 4262, 4116, 22040, 14602, 68016, 88376, 209936, 190746, 1062592, 839094, 2797000, 3728891, 11276704, 9587580, 67195520, 35792568
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OFFSET
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1,2
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COMMENTS
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Terms may be computed by filtering potentially isomorphic graphs of A056391 through nauty. Terms computed in this way for a(25), a(27) agree with theoretical calculations by others. - Andrew Howroyd, Apr 23 2017
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LINKS
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Victoria Gatt, Mikhail Klin, Josef Lauri, Valery Liskovets, From Schur Rings to Constructive and Analytical Enumeration of Circulant Graphs with Prime-Cubed Number of Vertices, in Isomorphisms, Symmetry and Computations in Algebraic Graph Theory, (Pilsen, Czechia, WAGT 2016) Vol. 305, Springer, Cham, 37-65.
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FORMULA
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There is an easy formula for prime orders. Formulae are also known for squarefree and prime-squared orders.
a(n) = A056391(n) for squarefree n.
(End)
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PROG
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(GAP)
LoadPackage("grape");
CirculantDigraphCount:= function(n) local g; # slow for n >= 10
g:=Graph( Group(()), [1..n], OnPoints, function(x, y) return (y-x) mod n = 1; end, false);
return Length(GraphIsomorphismClassRepresentatives(List(Combinations([1..n]), s->DistanceGraph(g, s))));
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CROSSREFS
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KEYWORD
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nonn,nice
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AUTHOR
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EXTENSIONS
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Further values for (twice) squarefree and (twice) prime-squared orders can be found in the Liskovets reference.
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STATUS
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approved
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