Calculate IBAN from Bank No. and Account No.


I need to calculate the IBAN from the bank no. and the account no. I know the algorithm, but one step is the MOD 97 operation of a 24 digit integer no. (here in Germany). I tried to use BigInteger and Decimal but got out of range. So the question would be: how could I calulate 500105170123456789131400 MOD 97? Or in the first place: how to create a variable that holds this BIG integer?