E.g.f. (1-x)/(1-4x).A052592E.g.f. (1-x)/(1-4x).Terms a(0) =1a(1) =3a(2) =24a(3) =288a(4) =4608a(5) =92160a(6) =2211840a(7) =61931520a(8) =1981808640a(9) =71345111040External referencesoeis: A052592