Evaluate the sum of reciprocals of double factorial of even nonnegative integers.

the taylor series for e^(x^2/2) is the sum of x^(2k)/(2k!!)  where !! is the double factorial, if you set x=1 we get the desired sum.  Thus the sum is equal to e^(1/2).

Posted by Daniel on 2018-06-22 21:36:18