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

Terms

a(0) =1a(1) =1a(2) =2a(3) =10a(4) =48a(5) =336a(6) =2400a(7) =22240a(8) =220416a(9) =2496256a(10) =30286080a(11) =411725568a(12) =6004838400a(13) =94609106944