%I A086677
%S A086677 1,4,31,360,5625,110880,2643795,74035080,2382538725,86656878000,
%T A086677 3515761193175,157425426358200,7711961781949425,410298436511964000,
%U A086677 23559634669682986875,1452240056377167057000,95649328231839993736125
%N A086677 Number of Steiner topologies on n points.
%D A086677 F. K. Hwang, D. S. Richards and P. Winter, The Steiner Tree Problem, 
               North-Holland, 1992, see p. 14.
%F A086677 Let f(n) = (2*n-4)!/(2^(n-2)*(n-2)!) (A001147) and let F(n, k) = binomial(n, 
               k+2) f(k) (n+k-2)! / (2k)!. Then a(n) = Sum_{k=0..n-2} Sum_{i=0..floor((n-k-2)/
               2)} binomial(n, i) F(n-i, k+i) (k+i)! / k!.
%Y A086677 Cf. A001147.
%Y A086677 Sequence in context: A136728 A102757 A145561 this_sequence A016036 A000314 
               A128709
%Y A086677 Adjacent sequences: A086674 A086675 A086676 this_sequence A086678 A086679 
               A086680
%K A086677 nonn,easy,nice
%O A086677 2,2
%A A086677 N. J. A. Sloane (njas(AT)research.att.com), Jul 28 2003
%E A086677 More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Jul 29 2003