Maxima Operator
!!
The double factorial operator.
For an integer, float, or rational number n
,
n!!
evaluates to the product n (n-2) (n-4) (n-6) ... (n - 2 (k-1))
where k
is equal to entier (n/2)
,
that is, the largest integer less than or equal to n/2
.
Note that this definition does not coincide with other published definitions
for arguments which are not integers.
For an even (or odd) integer n
, n!!
evaluates to the product of
all the consecutive even (or odd) integers from 2 (or 1) through n
inclusive.
For an argument n
which is not an integer, float, or rational,
n!!
yields a noun form genfact (n, n/2, 2)
.