a(n) = n! * [x^n] -exp(x^2)/(x - 1).

Terms

a(0) =1a(1) =1a(2) =4a(3) =12a(4) =60a(5) =300a(6) =1920a(7) =13440a(8) =109200a(9) =982800a(10) =9858240a(11) =108440640a(12) =1301952960a(13) =16925388480a(14) =236972736000