Finding next available number with addition of Left function

       -----A----- ------B------- C -----D------
   1     Number    W/ check digit   First Unused
   2   11242263959   112422639598    11242263965
   3   11242263960   112422639604               
   4   11242263961   112422639611               
   5   11242263962   112422639628               
   6   11242263963   112422639635               
   7   11242263964   112422639642               
   8   11242263966   112422639666               
   9   11242263967   112422639673               
  10   11242263968   112422639680

In D2, confirmed with Ctr+Shift+Enter,

=INT(INDEX(B2:B25, MATCH(TRUE, INT(B3:B25/10) - INT(B2:B24/10) > 1, 0))/10) + 1