Let's write down the consecutive terms of the sequence of natural numbers next to each other. Determine the 10000th digit of this number sequence.
The number of digits in the first 1000 numbers is $9 \cdot 1 + 90 \cdot 2 + 900 \cdot 3 + 4 = 2893$. Therefore, we still need to write $10000 - 2893 = 7107$ digits. Thus, we can add the numbers from 1001 to 2776, totaling 7104 digits, and the first three digits of the number 2777; hence, the 10000th digit is 7.

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The problem was also solved by: Bayer N., Chambrée M., Czukor G., Dénes M., Dőri V., Fried E., Füstös P., Grossberger Z., Kirchknopf E., Koffler B., Kovács Gy., Neumann L., Paunz A., Stolzer J., Szilárd V., Tandlich E., Viola R., Wáhl V.