Calculate IBAN from Bank No.

Hi,

I need to calculate the IBAN from the bank no. I know the algorithm, but one step is the MOD 97 operation of a 24 digit integer no. (Spain). I tried to use Int64 and Real but got out of range. So: how could I calulate 120345030000067890142800 MOD 97? Or in the first place: how to create a variable in AX that holds this BIG integer?

Thanks so much!