Coding challenge

Write some code to find how many three-digit numbers satisfy the property that the middle digit is the average of the first and the last digits. (Ans: 45.) (AMC 12A 2005.) Hint: use getdigit(x,n) to return the n$^{th}$ digit from the right of a number x. Ex: getdigit(1234,2) returns 3.

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Lua reference

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