Hi JGus,
in A1 =900000823 + Row() & "-1"
then fill down

If you need to start in some other cell, say C10 then use

in C10 =900000824 + Row() -ROW(B$10) & "-1"

the - ROW(B$10) can actually refer to any cell in row 10 but you must
put the $ sign before the 10. Also 900000824, not 900000823 in the
starting cell.

Ken Johnson