[ exp(4/7)*n! ].

Terms

a(0) =1a(1) =3a(2) =10a(3) =42a(4) =212a(5) =1274a(6) =8924a(7) =71398a(8) =642586a(9) =6425860a(10) =70684467a(11) =848213615a(12) =11026777001a(13) =154374878018