An alphametic is a type of cryptarithm in which a set of words is written down in the form of a long addition sum or some other mathematical problem. The object is to replace the letters of the alphabet with decimal digits to make a valid arithmetic sum. The word "alphametic" was coined in 1955 by James Hunter. However, the first modern alphametic, published by Henry Dudeney in the July 1924 issue of Strand Magazine, is "Send more money," or, setting it out in the form of a long addition:
and has the (unique) solution:
Two rules are obeyed by every alphametic. First, the mapping of letters to numbers is one-to-one; that is, the same letter always stands for the same digit, and the same digit is always represented by the same letter. Second, the digit zero isn't allowed as the left-most digit in any of the numbers being added or in their sum. The best alphametics are reckoned to be those with only one correct answer.