Calculate the double factorial of a number, or its logarithm.
DoubleFactorial(n)
DoubleFactorial64(n)
LnDoubleFactorial(n)
Log2DoubleFactorial(n)
LogDoubleFactorial(n)
LnDoubleFactorial.int(n)
LogDoubleFactorial.int(n)
Vector of integers.
Returns the double factorial, n * (n - 2) * (n - 4) * (n - 6) * ...
DoubleFactorial64()
: Returns the exact double factorial as a 64-bit
integer64
, for n
< 34.
LnDoubleFactorial()
: Returns the logarithm of the double factorial.
Log2DoubleFactorial()
: Returns the logarithm of the double factorial.
LnDoubleFactorial.int()
: Slightly faster, when x is known to be length one
and below 50001
Other double factorials:
doubleFactorials
,
logDoubleFactorials
DoubleFactorial (-4:0) # Return 1 if n < 2
#> [1] 1 1 1 1 1
DoubleFactorial (2) # 2
#> [1] 2
DoubleFactorial (5) # 1 * 3 * 5
#> [1] 15
exp(LnDoubleFactorial.int (8)) # log(2 * 4 * 6 * 8)
#> [1] 384
DoubleFactorial64(31)
#> integer64
#> [1] 191898783962510625