Chapter 2: Math, Angle, and Test Operations 81
nCr (number of combinations) returns the number of combinations of items taken number
at a time.
items and number must be nonnegative integers. Both items and number can be
lists.
items nCr number
Factorial
FactorialFactorial
Factorial
! (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)! = n…n!, 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!=n…(nN1)…(nN2)… ... …2…1, if n is an integer ‚ 0
n!= n…(nN1)…(nN2)… ... …1à2…‡p, if n+1à2 is an integer ‚ 0
n! is an error, if neither n nor n+1à2 is an integer ‚ 0.
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