code: public static String getBankNumberOfIban(final String pstring) {
      final String compressedIban = ibanCompress(pstring);
      final String country = StringUtils.substring(compressedIban, 0, 2);
      final IbanLengthDefinition length = IBAN_LENGTH_MAP.ibanLengths().get(country);
      return length == null ? null
          : StringUtils.substring(compressedIban, length.getBankNumberStart(),
              length.getBankNumberEnd());
    }
docs: get bank number of iban.
  
  @param pstring string with iban
  @return bank number