Texas Instruments TI-82 STATS Manual Book page 71

nPr,
nCr
! (Factorial)
(number of permutations) returns the number of
nPr
permutations of items taken number at a time. items and number
must be nonnegative integers. Both items and number can be
lists.
items number
nPr
(number of combinations) returns the number of
nCr
combinations of items taken number at a time. items and number
must be nonnegative integers. Both items and number can be
lists.
items number
nCr
(factorial) returns the factorial of either an integer or a multiple
!
of .5. For a list, it returns factorials for each integer or multiple
of .5. value must be ‚L.5 and 69.
value
!
Note: The factorial is computed recursively using the relationship
(n+1)! = nän!, until n is reduced to either 0 or L1/2. At that point, the
definition 0!=1 or the definition (L1à2)!=‡p is used to complete the
calculation. Hence:
n!=nä(nN1)ä(nN2)ä ... ä2ä1, if n is an integer ‚0
n!= nä(nN1)ä(nN2)ä ... ä1à2ä‡p, if n+1à2 is an integer ‚0
n! is an error, if neither n nor n+1à2 is an integer ‚0.
(The variable n equals value in the syntax description above.)
Math, Angle, and Test Operations 2.21