Robert J. answered 07/12/13
Certified High School AP Calculus and Physics Teacher
yn+1
= [(n+1)/(n+2)]yn
= [(n+1)/(n+2)][n/(n+1)]yn-1
= [(n+1)/(n+2)][n/(n+1)]...[1/2]y0, up to n = 1
= [1/(n+2)]y0, after canceling out (n+1)!
or
yn = [1/(n+1)]y0, if you substitute n for n+1.