The sum of the terms in the nth bracket of the series is
From n =1, we have
Sum of the terms in first bracket = 1
and
From n =2, we have
Sum of the terms in the second bracket = 2 + 3+4 =9
and ,
From n = 3, we have
Sum of the terms in the third bracket = (5 + 6 +7 +8+9) 35
and,