Hi,
I have a following formula in my Excel Form:
=IF(RIGHT(A1;1)=MID("0123456789ABCDEFHJKLMNPRSTUVWXY";MOD(LEFT(A1;6)&LEFT(RIGHT(A1;4);3);31)+1;1);"ok";"Error")
It validates the value in a cell A1. Data to be validated is Finnish social security number, like: 120365-5312 (fictional but ...