Automatic repeating sequence

[sheter]

I'm trying to automate my sheet numbers at the beginning of a project. Sometimes the building is so big we have to break it up into several sheets. For example, a project may need 3 sheets to display all of one floor. The sheet numbers for the 1st floor would be:
M101A
M101B
M101C

The second floor would be:
M102A
M102B
M102C

What would be great, is a way to automatically create this repeating sequence.

I've attached the file I'm trying to make.

THanks

 

[bosco_yip]

F4, copied down :

="M-"&101+INT((ROW(A1)-1)/C$3)&CHAR(65+MOD(ROW(A1)-1,C$3))

Regards
Bosco

 

[sheter]

Bosco,
This works like magic!!! Thank you, thank you!

sC.tt