题解 | 等差数列
import sys n = int(input()) a=2 l=[2,] if n ==1: print(2) else: for i in range(n-1): a = a+3 l.append(a) print(sum(l))
import sys n = int(input()) a=2 l=[2,] if n ==1: print(2) else: for i in range(n-1): a = a+3 l.append(a) print(sum(l))
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