[ exp(1/6)*n! ].

Terms

a(0) =1a(1) =2a(2) =7a(3) =28a(4) =141a(5) =850a(6) =5954a(7) =47632a(8) =428692a(9) =4286920a(10) =47156127a(11) =565873527a(12) =7356355863a(13) =102988982084