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 A054669 Triangular array giving number of even graphs with n nodes and k edges. 0
 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)
 OFFSET 1,10 REFERENCES F. Harary and E. Palmer, Graphical Enumeration, (1973). LINKS FORMULA 2^(-n)*(1+x)^C(n, 2)*Sum_{k=0..n} C(n, k)*((1-x)/(1+x))^(k*(n-k)). EXAMPLE [1],[1],[1,0,0,1],[1,0,0,4,3],[1,0,0,10,15,12,15,10,0,0,1],... CROSSREFS Cf. A033678. Sequence in context: A201636 A010102 A144161 * A131027 A133475 A021236 Adjacent sequences:  A054666 A054667 A054668 * A054670 A054671 A054672 KEYWORD easy,nonn,tabf,changed AUTHOR Vladeta Jovovic, Apr 18 2000 STATUS approved

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