Sequence summation 1 / 1 * 2 + 1 / 2 * 3 + 1 / 3 * 4 +... + 1 / 9 ^ 10

Sequence summation 1 / 1 * 2 + 1 / 2 * 3 + 1 / 3 * 4 +... + 1 / 9 ^ 10

1/1*2+1/2*3+1/3*4+...+1/9^10
=1-1/2+1/2-1/3+1/3-1/4+...+1/9-1/10
=1-1/10
=9/10