Series
Level
pending
Find the 2015th term of the series 1, 2, 6, 15, 31, 56, ... and then enter the answer modulo 1000.
The answer is 16.
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1 solution
T(n+1) = T(n) + n^2. Hence T(2015) = 1 + [2014 * 2015 ( 2*2014 + 1)/6], using the formula for summation of squares of natural numbers. It calculates to 2725088016. Ans: 16