E.g.f.: log(1 - x - log(1 - x)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =20a(6) =216a(7) =1862a(8) =13840a(9) =104904a(10) =949200a(11) =10517232a(12) =130307904a(13) =1694503824a(14) =23063845728a(15) =335427395760