题解 | #等差数列#
等差数列
https://www.nowcoder.com/practice/f792cb014ed0474fb8f53389e7d9c07f
while True:
try:
n = int(input())
sum = 2
for i in range(1, n):
number = 2 + 3 * i
sum += number
print(sum)
except:
break
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