Sequential Check Digit Validation

I have a spreadsheet that pulls in a log file after running a macro with 100000eight digit numbers which may or may not have a record in the system. These numbers are produced by using any seven digits and adding a check digit at the end for an eight digit number using the mod function specifically Mod7...=MOD(A1,7) , for example, if cell A1 has 1234567 the mod7 function will produce the check digit 5 then concatenating for the eight digit number 12345675. the next number will be produced by adding 1 to the end of the 7 digit number 1234567+1=1234568 then concatenating again the number with the check digit 6, 12345686. this would be sequential order.

my spreadsheet gets all the eight digit numbers with no record and sorts them in MOD7 sequential order in one column. since the spreadsheet ignores the eight digit numbers with records. my compiled list of numbers have non sequential numbers in the list.

i need a way in VB to loop through 100000 lines (column A) and find the first and last number of a MOD7 sequential range and place the first number in (column B) and the last in (column C).

I have figured a way to do this in a spreadsheet but it takes too many functions and calculations in 100000 lines so the spreadsheet takes too long to open and sometimes crashes!