Accumulation means that several items (usually 2 or 3 items) have the same item with opposite coefficients, such as an =1/n-1/(n+1) ... and an-1=1(n-6544

Then sn = a1+a2+a3+...+an =1-1/2+1/3+1/4. ..

Another example.

Bn= 1/n- 1/(n+2), then BN-1=1(n-1)-1(n+/kloc-0 . . sn = 1- 1/3+ 1/2- 1/4+ 1/3- 1/5+......+ 1/(n-2)- 1/n+ 1/(n- 1)- 1/(n+ / kloc-0/)+ 1/n- 1/(n+2)= 1+ 1/2- 1/(n+ 1)- 1

Cumulative multiplication is similar.

bn=n/(n+ 1)，bn- 1=(n- 1)/n，

cn=b 1*b2*b3*b4*.....* bn- 1 * bn = 1/2 * 2/3 * 3/4 *......(n- 1)/n * n/(n+ 1)= 1/(n+ 1) ...

bn=n/(n+2)，bn- 1 =(n- 1)/(n+ 1)，bn-2=(n-2)/n，

cn=b 1*b2*b3*....bn-2 * bn- 1 * bn = 1/3 * 2/4 * 3/5 * 4/6 *......*(n-2)/n *(n- 1)/(n+ 1)* n/(n+2)

= 1*2/((n+ 1)*(n+2))