The largest n-almost prime less than 3^n.

Terms

a(0) =2a(1) =6a(2) =20a(3) =60a(4) =208a(5) =624a(6) =2080a(7) =6240a(8) =18720a(9) =58240a(10) =176000a(11) =529408a(12) =1593344a(13) =4780032a(14) =14344192a(15) =43040768a(16) =129138688a(17) =387416064a(18) =1162248192a(19) =3486777344a(20) =10460332032a(21) =31380996096a(22) =94142988288a(23) =282428964864a(24) =847286894592