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%I #5 Aug 04 2014 11:06:19
%S 1,0,6,20,120,672,5516,40140,368640,3521870,37445298,422339502,
%T 5215454426,68144100780,954428684280,14160968076584,222769496190060,
%U 3692874342747114,64493471050666430,1181830474135532130,22692074431844298558,455404848204906308984
%N Number of preferential arrangements of n labeled elements such that the minimal number of elements per rank equals 2.
%H Alois P. Heinz, <a href="/A245855/b245855.txt">Table of n, a(n) for n = 2..400</a>
%F E.g.f.: 1/(2-exp(x)+x) -1/(2-exp(x)+x+x^2/2).
%F a(n) = A032032(n) - A102233(n) = A245732(n,2) - A245732(n,3).
%p b:= proc(n, k) option remember; `if`(n=0, 1,
%p add(b(n-j, k)*binomial(n, j), j=k..n))
%p end:
%p a:= n-> b(n, 2) -b(n, 3):
%p seq(a(n), n=2..25);
%Y Column k=2 of A245733.
%Y Cf. A032032, A102233, A245732.
%K nonn
%O 2,3
%A _Alois P. Heinz_, Aug 04 2014
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