Functions and CALL Routines 
Computes the number of permutations of n items that
are taken r at a time.

n

is an integer that represents the total
number of elements from which the sample is chosen.

r

is an integer value that represents the
number of chosen elements. If r is omitted, the function returns
the factorial of n.
Restriction: 
r n 
The mathematical representation of the
PERM function is given by the following equation:
with n 0, r 0, and n r.
If the expression cannot be computed, a missing value
is returned. For moderately large values, it is sometimes not possible to
compute the PERM function.
SAS Statements 
Results 
x=perm(5,1);

5

x=perm(5);

120

x=perm(5,2)

20

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