In an alphametic, letters are substituted for numbers in an arithmetic problem, and the reader is invited to find the solution. If the letters spell out some sort of a message, so much the better; the oldest one known, SEND + MORE = MONEY, was crafted by H.E. Dudeney in 1924. (The term alphametic was coined by J.A.H. Hunter in 1955.)
"Some Narrative Alphametics,"
Word Ways: Vol. 39
, Article 13.
Available at: http://digitalcommons.butler.edu/wordways/vol39/iss3/13