Take integer [78] in the sequence for instance : ...73 74 75 76 [78] 79 81 82 83...

The digit "7", jumping 7 digits back, ends on "3" [73] which is not "7"; jumping 7 digits to the right ends on "2" which, again, is not a "7". The same can be said for "8" (left -> "7"; right -> "3")