1.先创造等差数列
2.然后把等差数列累加
n = int(input()) init = 2 interval = 3 res = 0 for each in range(2, 2 + n * interval, interval): res += each print(res)
n = int(input()) init = 2 interval = 3 res = 0 for each in range(2, 2 + n * interval, interval): res += each print(res)