van=facebook.com/LearningCalculus$

f(i):=1/(i*(i+1));

create_list(f(i), i,  1,  4);
create_list(f(i), i, 16, 19);

sum(1/(i*(i+1)),i,1,19);

floor(%);

f(x);

g(n):=sum(1/(i*(i+1)),i,1,n)=n/(n+1);

rhs(g(x));