[ exp(2/13)*n! ].

Terms

a(0) =1a(1) =2a(2) =6a(3) =27a(4) =139a(5) =839a(6) =5878a(7) =47025a(8) =423231a(9) =4232310a(10) =46555420a(11) =558665046a(12) =7262645598a(13) =101677038385