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A054669
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Triangular array giving number of even graphs with n nodes and k edges.
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0
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1, 1, 1, 0, 0, 1, 1, 0, 0, 4, 3, 1, 0, 0, 10, 15, 12, 15, 10, 0, 0, 1, 1, 0, 0, 20, 45, 72, 160, 240, 195, 120, 96, 60, 15, 1, 0, 0, 35, 105, 252, 805, 1935, 3255, 4515, 5481, 5481, 4515, 3255, 1935, 805, 252, 105, 35, 0, 0, 1, 1, 0, 0, 56, 210, 672, 2800, 9320, 24087
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,10
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REFERENCES
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F. Harary and E. Palmer, Graphical Enumeration, (1973).
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LINKS
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Table of n, a(n) for n=1..66.
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FORMULA
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2^(-n)*(1+x)^C(n, 2)*Sum_{k=0..n} C(n, k)*((1-x)/(1+x))^(k*(n-k)).
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EXAMPLE
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[1],[1],[1,0,0,1],[1,0,0,4,3],[1,0,0,10,15,12,15,10,0,0,1],...
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CROSSREFS
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Cf. A033678.
Sequence in context: A201636 A010102 A144161 * A131027 A133475 A021236
Adjacent sequences: A054666 A054667 A054668 * A054670 A054671 A054672
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KEYWORD
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easy,nonn,tabf,changed
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AUTHOR
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Vladeta Jovovic, Apr 18 2000
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STATUS
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approved
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