7*n analog to Keith numbers.

Terms

a(0) =3a(1) =6a(2) =9a(3) =12a(4) =25a(5) =29a(6) =33a(7) =58a(8) =62a(9) =66a(10) =70a(11) =87a(12) =91a(13) =95a(14) =99a(15) =124a(16) =128a(17) =150a(18) =152a(19) =165a(20) =178a(21) =191a(22) =204a(23) =217a(24) =592a(25) =801a(26) =1184a(27) =3860a(28) =15728a(29) =59800