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A053467
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Number of directed 2-multigraphs on n nodes.
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3
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1, 6, 138, 22815, 29197989, 286181094816, 21712697070199704, 12980080058620326927885, 62082385554465497895132149640, 2405193620328895144597707267893468286
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| A 2-multigraph is similar to an ordinary graph except there are 0, 1 or 2 edges between any two nodes (self-loops are not allowed).
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MATHEMATICA
| Table[CycleIndex[PairGroup[SymmetricGroup[n], Ordered], t] /.Table[t[i] -> 1 + x^i + y^i, {i, 1, n^2}] /. {x -> 1, y -> 1}, {n, 1, 7}] (* Geoffrey Critzer, Mar 8 2011 *)
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CROSSREFS
| Cf. A000273.
Sequence in context: A075185 A003994 A155558 * A090944 A007340 A122483
Adjacent sequences: A053464 A053465 A053466 * A053468 A053469 A053470
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KEYWORD
| easy,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 13 2000
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