code: public static boolean alg_74(int[] blz, int[] number) {
          int sum = addProducts(number, 0, 8, new int[]{2, 1, 2, 1, 2, 1, 2, 1, 2}, true);
          int crc = (10 - sum % 10) % 10;
          if (number[9] == crc) {
              return true;
          }
  
          if (number[0] + number[1] + number[2] + number[3] == 0 && number[4] != 0) {
              crc = (5 - sum % 5);
              return number[9] == crc;
          }
  
          return false;
      }
docs: TODO: more tests