1, the unit number is "1": quick calculation formula: head multiplied by head, head plus head, mantissa is 1 (if head plus head exceeds 10, carry it).

2. Decimal digit is "1": quick calculation formula: the head is 1, the tail is added, and the tail is multiplied by the tail (more than 10, carry).

3. Every single digit is "9": quick calculation formula: each person adds 1, multiplies 10, subtracts the added number, and finally puts 1.

4. Ten digits are all "9": quick calculation formula: 100 minus the previous number, and then minus the latter number. 100 MINUS everyone, the results are multiplied by each other, accounting for 2 places.

5. The heads are the same and the tails are complementary (the mantissas add up to 10): a quick formula: the head is multiplied by the head 1 and the tail is multiplied by the tail 2 digits.

6, the heads are complementary, the tails are the same: quick calculation formula: the head is multiplied by the head, and the tail is multiplied by the tail, accounting for 2 digits.

7. Multiply the remainder by the number of iterations: quick calculation formula: head plus 1 head again, and tail after tail accounts for 2.

8. One of them is 1 1: the quick formula: the beginning and the end are fixed, and the middle is added.