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

**x^3 + y^3 + z^3 = w^3**.

The smallest set of positive integers x,y,z,w qualifying as a solution of the bolded equation above is: **
3,4,5,6 **

a.Find some other sets of distinct integers, not necessarily positive.

b. Provide some comments on "The sum of 3 cubes is a cube" equation.