If d,e are consecutive digits of n in base 7, then |d-e|>=4.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =6a(6) =12a(7) =13a(8) =20a(9) =28a(10) =35a(11) =36a(12) =42a(13) =43a(14) =44a(15) =84a(16) =85a(17) =91a(18) =92a(19) =93a(20) =140a(21) =141a(22) =142a(23) =200a(24) =201a(25) =202a(26) =249a(27) =250a(28) =251a(29) =257