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A104653
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Number of topologically distinct trees with n vertices, including Steiner trees.
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0
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0, 1, 4, 27, 270, 3645, 62370, 1295595, 31689630, 892387125, 28439784450, 1011998000475, 39773696712750, 1711186282730925, 79990996596761250, 4037168079574504875, 218797477268743122750, 12673229445076108033125
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| Let F(n,s) = number of Steiner trees with n vertices and s Steiner points; then A001147 is also F(n,n-2) for n>2. - Robert G. Wilson v (rgwv(AT)rgwv.com), May 10 2005
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REFERENCES
| Gilbert, E. N. and Pollak, H. O. (1968) Steiner minimal trees. SIAM Journal of Applied Mathematics, 16: 1-29.
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FORMULA
| a(1) = 0 a(2) = 1 a(n) = sum indexed on s(0 to n-2; 2^s * binomial(n, s+2) * (n+s-2)!/s!
a(1) = 0, a(2) = 1; a(n) = sum_{s=0..n-2} (2^-s)* binomial(n, s+2)*(n+s-2)!/s!. - Robert G. Wilson v (rgwv(AT)rgwv.com), May 10 2005
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EXAMPLE
| Let F(n,s) = number of Steiner trees with n vertices and s Steiner points. Then a(3)=4 because we can have F(3,0)=3 and F(3,1)=1
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MATHEMATICA
| f[n_] := Sum[ Binomial[n, k + 2](n + k - 2)!/(k!2^k), {k, 0, n - 2}]; Table[ f[n], {n, 18}] (from Robert G. Wilson v (rgwv(AT)rgwv.com), May 10 2005)
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CROSSREFS
| Cf. A001147.
Sequence in context: A121353 A161633 A052871 * A194787 A020558 A193467
Adjacent sequences: A104650 A104651 A104652 * A104654 A104655 A104656
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KEYWORD
| easy,nonn
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AUTHOR
| Alexandre Goncalves (alexg(AT)civil.ist.utl.pt), Apr 22 2005
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), May 10 2005
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