The PERM function calculates the number of permutations of n distinct things taken m at a time, using the following formula:
PERM = FACT(n) / FACT(n - m)
For example, to get the number of permutations of the three letters a, b and c, taking 2 at a time, use the formula:
PERM(3, 2)
which returns 6. The six permutations are ab, ac, bc, ba, ca, cb.
A more complex example is a coded telegram where each word is 5 letters in length. The number of possible different words, where each word contains a letter no more than once, is given by the formula:
PERM(26, 5)
which returns 7893600.
See also: