[ exp(2/9)*n! ].

Terms

a(0) =1a(1) =2a(2) =7a(3) =29a(4) =149a(5) =899a(6) =6294a(7) =50353a(8) =453182a(9) =4531822a(10) =49850050a(11) =598200606a(12) =7776607883a(13) =108872510366