(1+3^n)*n!.A052573(1+3^n)*n!.Terms a(0) =2a(1) =4a(2) =20a(3) =168a(4) =1968a(5) =29280a(6) =525600a(7) =11027520a(8) =264579840a(9) =7142929920a(10) =214280640000External referencesoeis: A052573