a(n) = 3*a(n-1), with a(1) = 20.

Terms

a(0) =20a(1) =60a(2) =180a(3) =540a(4) =1620a(5) =4860a(6) =14580a(7) =43740a(8) =131220a(9) =393660a(10) =1180980a(11) =3542940a(12) =10628820a(13) =31886460a(14) =95659380a(15) =286978140a(16) =860934420a(17) =2582803260a(18) =7748409780a(19) =23245229340a(20) =69735688020a(21) =209207064060a(22) =627621192180