E.g.f.: Product_{k>0} (1 + tanh(x^k/k)).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =14a(5) =70a(6) =364a(7) =2548a(8) =21104a(9) =189936a(10) =1830968a(11) =20140648a(12) =241712272a(13) =3142259536a(14) =43472528384a(15) =652087925760