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%I #22 Apr 17 2015 14:37:34
%S 0,0,1,18,300,5550,117780,2873262,80126228,2534723280,90239747220,
%T 3588582531875,158318375911740,7700793136255440,410691133882551795,
%U 23894146232727414630,1509723335738373490800,103169903975944947302744,7597003720932150826636260,600748548233457344454385722
%N Binomial(n,2)*B(n-1)*(B(n)-B(n-1)), where B() = A000110() are the Bell numbers.
%C Sum of the Rand distance over all unordered pairs of partitions.
%H Frank Ruskey and Jennifer Woodcock, <a href="http://dx.doi.org/10.1007/978-3-642-25011-8_23">The Rand and block distances of pairs of set partitions</a>, Combinatorial algorithms, 287-299, Lecture Notes in Comput. Sci., 7056, Springer, Heidelberg, 2011.
%t Table[Binomial[n, 2]*BellB[n - 1] (BellB[n] - BellB[n - 1]), {n, 19}] (* _Michael De Vlieger_, Apr 16 2015 *)
%Y Cf. A000110, A191200.
%Y Equals half A124104.
%K nonn
%O 0,4
%A _N. J. A. Sloane_, Aug 26 2011