Number of permutations in S_n with longest increasing subsequence of length <= 3 (i.e. 1234-avoiding permutations); vexillary permutations (i.e. 2143-avoiding).
1, 1, 2, 6, 23, 103, 513, 2761, 15767, 94359, 586590, 3763290, 24792705
1 seqfan posts
Mon Jun 8 05:50:00 CEST 2009 [seqfan] Re: perms and set partitions