Floor( exp(13/21)*n! ).

Terms

a(0) =1a(1) =3a(2) =11a(3) =44a(4) =222a(5) =1337a(6) =9360a(7) =74880a(8) =673925a(9) =6739256a(10) =74131823a(11) =889581881a(12) =11564564464a(13) =161903902509