79. There is a ten-digit number. Counting from left to right, if its first digit is a certain number, then this ten-digit number contains that many 0s; if its second digit is a certain number, then this ten-digit number contains that many 1s; if its third digit is a certain number, then this ten-digit number contains that many 2s; ...; if its tenth digit is a certain number, then this ten-digit number contains that many 9s. This ten-digit number is . $\qquad$
Answer: 6210001000