Signed super-Catalan or little Schroeder numbers.

Terms

a(0) =1a(1) =-1a(2) =3a(3) =-11a(4) =45a(5) =-197a(6) =903a(7) =-4279a(8) =20793a(9) =-103049a(10) =518859a(11) =-2646723a(12) =13648869a(13) =-71039373a(14) =372693519a(15) =-1968801519a(16) =10463578353a(17) =-55909013009a(18) =300159426963