The (3^n)-th composite number.

Terms

a(0) =4a(1) =8a(2) =16a(3) =40a(4) =111a(5) =306a(6) =882a(7) =2563a(8) =7513a(9) =22170a(10) =65602a(11) =194695a(12) =578949a(13) =1724117a(14) =5140568a(15) =15340177a(16) =45811041a(17) =136886318a(18) =409221920a(19) =1223856725a(20) =3661401440a(21) =10956876415a(22) =32796782398a(23) =98189738332a(24) =294021666926a(25) =880564233896