[ exp(3/20)*n! ].

Terms

a(0) =1a(1) =2a(2) =6a(3) =27a(4) =139a(5) =836a(6) =5855a(7) =46845a(8) =421606a(9) =4216064a(10) =46376705a(11) =556520461a(12) =7234765995a(13) =101286723938