A palindrome is a number which is the same if its digits are reversed, e. g., 77, 232, 1331. The digit 0 is not used at the beginning or end of a palindrome, but can be used in the middle, e. g., 0110 is not allowed, but 1001, 303 are. The nine single-digit numbers 1, 2, 3, . . . , 9 are the simplest palindromes. Similarly, there are nine 2-digit palindromes, 11, 22, 33, . . . , 99. How many 3-digit palindromes are there?

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