="1234"&TEXT(ROWS($1:1),"000000")&"5678"

Adjust to suit
copy down as far as needed


"how can i sequence the middle numbers" wrote:

I have to make 1000 numbers for some gift cards magnetic strip. the numbers
are 14 digits long and the middle 6 numbers are sequential. the first and
last four numbers stay the same for all 1000. The numbers have to be in one
row in excel sot that it can be transfered to the card making machine. how
can i do this without typing all 1000 numbers?