E.g.f.: exp(x/(1 - 4*x)).A321847E.g.f.: exp(x/(1 - 4*x)).Terms a(0) =1a(1) =1a(2) =9a(3) =121a(4) =2161a(5) =48081a(6) =1279801a(7) =39631369a(8) =1398961761a(9) =55422807841External referencesoeis: A321847