1. The problem asks for the digit that names the number of thousands in the number 19971861990. 2. To find the digit representing thousands, we look at the fourth digit from the right in the number. 3. The number is 19971861990. 4. Counting digits from right to left: 0 (ones), 9 (tens), 9 (hundreds), 1 (thousands). 5. Therefore, the digit naming the number of thousands is 1.