#6**+5 **

Double factorial (aka semifactorial) is a mathematical operation in which one multiplies "every other" natural number up to a given number. A more precise definition is:

$$n!!=\prod \limits_{i=0}^{k}(n-2i)= n(n-2)(n-4)(n-6)...$$

Where k = (n/2) - 1

Or read more on the "Double Factorial" Wikipedia web page :)

Tetration Jan 10, 2015

#1**+5 **

How about:

4 + √4 +√4 +√4

Technically speaking you've used two's since √x = ^{2}√x

Tetration Jan 9, 2015

#6**+5 **

Best Answer

Double factorial (aka semifactorial) is a mathematical operation in which one multiplies "every other" natural number up to a given number. A more precise definition is:

$$n!!=\prod \limits_{i=0}^{k}(n-2i)= n(n-2)(n-4)(n-6)...$$

Where k = (n/2) - 1

Or read more on the "Double Factorial" Wikipedia web page :)

Tetration Jan 10, 2015