[ exp(2/15)*n! ].

Terms

a(0) =1a(1) =2a(2) =6a(3) =27a(4) =137a(5) =822a(6) =5758a(7) =46070a(8) =414637a(9) =4146378a(10) =45610165a(11) =547321987a(12) =7115185831a(13) =99612601644