The number of even separable permutations of length n.

Terms

a(0) =1a(1) =1a(2) =3a(3) =12a(4) =48a(5) =197a(6) =903a(7) =4298a(8) =20862a(9) =103049a(10) =518859a(11) =2647296a(12) =13651092a(13) =71039373a(14) =372693519a(15) =1968822294a(16) =10463661690a(17) =55909013009a(18) =300159426963