a(n) = C(n+2,2)*(2*n)!/2^n.A132912a(n) = C(n+2,2)*(2*n)!/2^n.Terms a(0) =1a(1) =3a(2) =36a(3) =900a(4) =37800a(5) =2381400a(6) =209563200a(7) =24518894400External referencesoeis: A132912