[ exp(4/5)*n! ].

Terms

a(0) =2a(1) =4a(2) =13a(3) =53a(4) =267a(5) =1602a(6) =11216a(7) =89733a(8) =807604a(9) =8076042a(10) =88836472a(11) =1066037665a(12) =13858489652a(13) =194018855141