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A213269
The number of edges in the directed graph of the 2-opt landscape of the symmetric TSP
0
0, 6, 60, 540, 5040, 50400, 544320, 6350400, 79833600, 1077753600, 15567552000, 239740300800, 3923023104000, 67999067136000, 1244905998336000, 24008901396480000, 486580401635328000, 10339833534750720000, 229909239772692480000, 5339003456943636480000
OFFSET
3,2
REFERENCES
J. W. Barnes, B. Dimova, S. P. Dokov, A. Solomon, The theory of elementary landscapes. Applied Mathematics Letters, 16(3):337-343, 2003.
FORMULA
a(n) = n!*(n-3)/4
EXAMPLE
For a 3 city TSP n=3 there are no edges in the landscape.
For a 4 city TSP there are 6 edges in the directed graph of the 2-opt landscape.
MATHEMATICA
Table[(n!(n-3))/4, {n, 3, 30}] (* Harvey P. Dale, Oct 15 2016 *)
PROG
(GAP)
edges:=n->Factorial(n)*(n-3)/4;
List([3..30], edges);
CROSSREFS
Sequence in context: A248217 A102232 A121113 * A091710 A054880 A186656
KEYWORD
nonn,easy
AUTHOR
Paul John Sutcliffe, Jun 07 2012
STATUS
approved