cp's OEIS Frontend

A245855 Number of preferential arrangements of n labeled elements such that the minimal number of elements per rank equals 2.

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