3-nonnesting permutations.

Terms

a(0) =1a(1) =2a(2) =6a(3) =24a(4) =118a(5) =675a(6) =4333a(7) =30464a(8) =230615a(9) =1856336a(10) =15738672a(11) =139509303a(12) =1285276242a(13) =12248071935a(14) =120255584181