a(n) = floor( exp(14/17)*n! ).

Terms

a(0) =2a(1) =4a(2) =13a(3) =54a(4) =273a(5) =1640a(6) =11483a(7) =91870a(8) =826832a(9) =8268320a(10) =90951527a(11) =1091418329a(12) =14188438288a(13) =198638136041