Will someone please enlighten me as to the proper AWG Copper and number of conductors for 40 AMP electric range cable? Thank you for your consideration.

2 #8's for hots, a #10 for Neutral and a #10 for ground. On a 40 Amp breaker.
Many times I just pull #6, and reduce breaker from 50 to 40 if needed. This will go to a 4 wire receptacle, and range should be wired with a 4 wire cord.

If you are not in an area that requires the use of conduit, such as Chicagoland, 8/3NM cable is standard issue for this.

Some folks do run 6/3 like Strat suggested. This is only required if you think there is the possibility of getting a very large unit (over 12Kw) in the future.

ANY unit 12Kw and under you can use 8/3 on a 40A breaker.