[ exp(1/18)*n! ].

Terms

a(0) =1a(1) =2a(2) =6a(3) =25a(4) =126a(5) =761a(6) =5327a(7) =42623a(8) =383610a(9) =3836105a(10) =42197156a(11) =506365881a(12) =6582756454a(13) =92158590368