E.g.f.: Product_{k>=1} (1 + tan(x^k)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =14a(4) =48a(5) =416a(6) =3360a(7) =29504a(8) =274176a(9) =3503104a(10) =45192960a(11) =579956992a(12) =8982251520a(13) =138130720768