Theosophical reduction

Theosophical reduction is the basic operation of numerology: the digits of a number are added together until only a single digit remains. Thus 1987 gives 1 + 9 + 8 + 7 = 25, then 2 + 5 = 7. Most schools stop before the last step when they reach a master number (11, 22, sometimes 33). The term comes from late 19th-century occultism, which saw in it the return of every quantity to its essence.