J. Noonan et D. Zeilberger, THE ENUMERATION OF PERMUTATIONS WITH A PRESCRIBED NUMBER OF FORBIDDENPATTERNS, Advances in applied mathematics, 17(4), 1996, pp. 381-407
We initiate a general approach for the fast enumeration of permutation
s with a prescribed number of occurrences of ''forbidden'' patterns th
at seems to indicate that the enumerating sequence is always P-recursi
ve. We illustrate the method completely in terms of the patterns ''abc
,'' ''cab,'' and ''abcd.'' (C) 1996 Academic Press, Inc.