Sphenic numbers having identical digits.

Terms

a(0) =66a(1) =222a(2) =555a(3) =777a(4) =2222a(5) =3333a(6) =5555a(7) =7777a(8) =22222a(9) =33333a(10) =55555a(11) =77777a(12) =2222222a(13) =3333333a(14) =5555555a(15) =7777777a(16) =22222222222a(17) =33333333333a(18) =55555555555a(19) =77777777777