Composite numbers whose prime factors contain no digits other than 6 and 7.

Terms

a(0) =49a(1) =343a(2) =469a(3) =2401a(4) =3283a(5) =4489a(6) =4739a(7) =16807a(8) =22981a(9) =31423a(10) =33173a(11) =45359a(12) =117649a(13) =160867a(14) =219961a(15) =232211a(16) =300763a(17) =317513a(18) =458329a(19) =474439a(20) =536669a(21) =537439a(22) =823543a(23) =1126069a(24) =1539727a(25) =1625477a(26) =2105341a(27) =2222591a(28) =3039053a(29) =3208303