A Nice Factorial Problem 

2exp-8 should have been a more elegant form of the result in my mind.

That's the hard way

( 15! )/( 17! - 16! ) = ( 15! )/15! ( 16 ×17 - 16 ) = 1/16 ( 17 - 1 ) = 1/(16x16) = = 1/( 2^4 × 2^4 ) = 1/( 2^8 ) = 2^( - 8 )