5 digit numbers where the sum is equal to 18

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You could list the numbers 99 to 99000 (this is an Excel 2007+ exercise) down a column starting in A2 . In the B2 and copy down,

=SUM(--MID(A2, ROW(INDIRECT("1:" & LEN(A2))), 1))

... confirmed with Ctrl+Shift+Enter

In C2 and down

=A2=18

AutoFilter col C for FALSE, clear those cells, unAutoFilter, and sort by col A:

       -A- -B- -C--
   1   Num Sum 18? 
   2    99  18 TRUE
   3   189  18 TRUE
   4   198  18 TRUE
   5   279  18 TRUE
   6   288  18 TRUE
   7   297  18 TRUE
   8   369  18 TRUE
   9   378  18 TRUE
  10   387  18 TRUE
  11   396  18 TRUE
  12   459  18 TRUE
  13   468  18 TRUE
  14   477  18 TRUE
  15   486  18 TRUE
  16   495  18 TRUE

There are 3915 numbers left in the list.