1/n(n+1)(n+2)=[1/n(n+1)-1/(n+1)(n+2)]/2
1/1*2*3+1/2*3*4+...+1/97*98*99
=(1/1*2-1/2*3+1/2*3-1/3*4+.+1/97*98-1/98*99)/2
=(1/2-1/98*99)/2
=2425/9702