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A031878
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Maximal number of edges in Hamiltonian path in complete graph on n nodes.
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3
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0, 1, 3, 5, 10, 13, 21, 25, 36, 41, 55, 61, 78, 85, 105, 113, 136, 145, 171, 181, 210, 221, 253, 265, 300, 313, 351, 365, 406, 421, 465, 481, 528, 545, 595, 613, 666, 685, 741, 761, 820, 841, 903, 925, 990, 1013, 1081, 1105, 1176, 1201, 1275, 1301, 1378
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OFFSET
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1,3
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COMMENTS
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Given a regular polygon with n sides, a(n) is the number of circles that have an edge of the polygon as a diameter (5 for n=4, 10 for n=5, 13 for n=6, ...). - Ahmet Arduç, Jan 28 2017
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LINKS
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FORMULA
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a(n) = C(n, 2) if n odd, a(n) = C(n, 2)-n/2+1 if n even.
G.f.: x^2*(1+2*x+x^3)/((1-x)*(1-x^2)).
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EXAMPLE
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E.g. for n=4 [1:2][2:3][3:1][1:4][4:2], so a(4) = 5.
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MATHEMATICA
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LinearRecurrence[{1, 2, -2, -1, 1}, {0, 1, 3, 5, 10}, 60] (* Harvey P. Dale, Mar 14 2015 *)
CoefficientList[ Series[-x (x^3 + 2x + 1)/((x - 1)^3 (x + 1)^2), {x, 0, 52}], x] (* Robert G. Wilson v, Jul 30 2018 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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