2. The number 98 is written on the board. Every minute, the number is erased and replaced with the product of its digits, increased by 15. What number will be on the board after an hour?
Solution. Starting from the fourth minute, a periodic sequence with a period length of 6 is formed: 98, 87, 71, 22, 19, 24, 23, 21, 17, 22, ..

On the 60th minute, just like on the 6th minute, the number 24 will appear on the board, and therefore, after an hour, that is, on the 61st minute, the number 23 will be on the board.

Comment. The periodic sequence is correctly identified - 4 points.