Composite numbers whose prime factors contain no digits other than 1 and 7.

Terms

a(0) =49a(1) =77a(2) =119a(3) =121a(4) =187a(5) =289a(6) =343a(7) =497a(8) =539a(9) =781a(10) =833a(11) =847a(12) =1207a(13) =1309a(14) =1331a(15) =2023a(16) =2057a(17) =2401a(18) =3179a(19) =3479a(20) =3773a(21) =4913a(22) =5041a(23) =5467a(24) =5831a(25) =5929a(26) =7819a(27) =8197a(28) =8449a(29) =8591