Increasing gaps between 3-smooth numbers (lower end).

Terms

a(0) =1a(1) =4a(2) =9a(3) =12a(4) =18a(5) =36a(6) =81a(7) =108a(8) =162a(9) =256a(10) =288a(11) =324a(12) =512a(13) =576a(14) =648a(15) =768a(16) =864a(17) =1024a(18) =1152a(19) =1296a(20) =1536a(21) =1728a(22) =2304a(23) =2592a(24) =3072a(25) =3456a(26) =4608a(27) =5184a(28) =6912a(29) =9216