adding numeric portion of alphanumeric cell

i have a field like

ABC_AN_2001006

the next field will be AB_AN_2001007
and so on just add 1

so i need to come up with something that lets me just drag and get the result
is there any other way then concatenate to do this.

If you click in the lower right corner of the cell containing the alphanumeric figure and drag down, does that not add 1 to the previous entry? (Because it does work on my excel)

yes that works but the problem is i don't need to add 1, i need to add 1000
and sometimes a different number