[ exp(7/9)*n! ].

Terms

a(0) =2a(1) =4a(2) =13a(3) =52a(4) =261a(5) =1567a(6) =10970a(7) =87761a(8) =789855a(9) =7898554a(10) =86884101a(11) =1042609219a(12) =13553919858a(13) =189754878021