Which of the following is the sum of the sequence 1,4,7,…,3n−21, 4, 7, \dots, 3n-21,4,7,…,3n−2?
n(3n−1)2\frac{n(3n-1)}{2}2n(3n−1)
n(3n+1)2\frac{n(3n+1)}{2}2n(3n+1)
n(3n−2)2\frac{n(3n-2)}{2}2n(3n−2)
n(3n−1)n(3n-1)n(3n−1)